Display generic function signature properly (#19544)

## Summary

Resolves https://github.com/astral-sh/ty/issues/817

## Test Plan

Update mdtest

---------

Co-authored-by: Carl Meyer <carl@astral.sh>

crates/ty_python_semantic/resources/mdtest/generics/scoping.md

@@ -152,7 +152,7 @@ already solved and specialized when the class was specialized:
 from ty_extensions import generic_context
 
 legacy.m("string", None)  # error: [invalid-argument-type]
-reveal_type(legacy.m)  # revealed: bound method Legacy[int].m(x: int, y: S@m) -> S@m
+reveal_type(legacy.m)  # revealed: bound method Legacy[int].m[S](x: int, y: S@m) -> S@m
 reveal_type(generic_context(Legacy))  # revealed: tuple[T@Legacy]
 reveal_type(generic_context(legacy.m))  # revealed: tuple[S@m]
 ```

crates/ty_python_semantic/resources/mdtest/scopes/builtin.md

@@ -11,7 +11,7 @@ def _(flag: bool) -> None:
         abs = 1
         chr: int = 1
 
-    reveal_type(abs)  # revealed: Literal[1] | (def abs(x: SupportsAbs[_T@abs], /) -> _T@abs)
+    reveal_type(abs)  # revealed: Literal[1] | (def abs[_T](x: SupportsAbs[_T@abs], /) -> _T@abs)
     reveal_type(chr)  # revealed: Literal[1] | (def chr(i: SupportsIndex, /) -> str)
 ```
 

crates/ty_python_semantic/resources/mdtest/snapshots/union_call.md_-_Calling_a_union_of_f…_-_Try_to_cover_all_pos…_-_Cover_non-keyword_re…_(707b284610419a54).snap

@@ -86,7 +86,7 @@ error[call-non-callable]: Object of type `Literal[5]` is not callable
    |         ^^^^
    |
 info: Union variant `Literal[5]` is incompatible with this call site
-info: Attempted to call union type `(def f1() -> int) | (def f2(name: str) -> int) | (def f3(a: int, b: int) -> int) | (def f4(x: T@f4) -> int) | Literal[5] | (Overload[() -> None, (x: str) -> str]) | (Overload[() -> None, (x: str, y: str) -> str]) | PossiblyNotCallable`
+info: Attempted to call union type `(def f1() -> int) | (def f2(name: str) -> int) | (def f3(a: int, b: int) -> int) | (def f4[T: str](x: T@f4) -> int) | Literal[5] | (Overload[() -> None, (x: str) -> str]) | (Overload[() -> None, (x: str, y: str) -> str]) | PossiblyNotCallable`
 info: rule `call-non-callable` is enabled by default
 
 ```
@@ -101,7 +101,7 @@ error[call-non-callable]: Object of type `PossiblyNotCallable` is not callable (
    |         ^^^^
    |
 info: Union variant `PossiblyNotCallable` is incompatible with this call site
-info: Attempted to call union type `(def f1() -> int) | (def f2(name: str) -> int) | (def f3(a: int, b: int) -> int) | (def f4(x: T@f4) -> int) | Literal[5] | (Overload[() -> None, (x: str) -> str]) | (Overload[() -> None, (x: str, y: str) -> str]) | PossiblyNotCallable`
+info: Attempted to call union type `(def f1() -> int) | (def f2(name: str) -> int) | (def f3(a: int, b: int) -> int) | (def f4[T: str](x: T@f4) -> int) | Literal[5] | (Overload[() -> None, (x: str) -> str]) | (Overload[() -> None, (x: str, y: str) -> str]) | PossiblyNotCallable`
 info: rule `call-non-callable` is enabled by default
 
 ```
@@ -116,7 +116,7 @@ error[missing-argument]: No argument provided for required parameter `b` of func
    |         ^^^^
    |
 info: Union variant `def f3(a: int, b: int) -> int` is incompatible with this call site
-info: Attempted to call union type `(def f1() -> int) | (def f2(name: str) -> int) | (def f3(a: int, b: int) -> int) | (def f4(x: T@f4) -> int) | Literal[5] | (Overload[() -> None, (x: str) -> str]) | (Overload[() -> None, (x: str, y: str) -> str]) | PossiblyNotCallable`
+info: Attempted to call union type `(def f1() -> int) | (def f2(name: str) -> int) | (def f3(a: int, b: int) -> int) | (def f4[T: str](x: T@f4) -> int) | Literal[5] | (Overload[() -> None, (x: str) -> str]) | (Overload[() -> None, (x: str, y: str) -> str]) | PossiblyNotCallable`
 info: rule `missing-argument` is enabled by default
 
 ```
@@ -152,7 +152,7 @@ info: Overload implementation defined here
 28 |     return x + y if x and y else None
    |
 info: Union variant `Overload[() -> None, (x: str, y: str) -> str]` is incompatible with this call site
-info: Attempted to call union type `(def f1() -> int) | (def f2(name: str) -> int) | (def f3(a: int, b: int) -> int) | (def f4(x: T@f4) -> int) | Literal[5] | (Overload[() -> None, (x: str) -> str]) | (Overload[() -> None, (x: str, y: str) -> str]) | PossiblyNotCallable`
+info: Attempted to call union type `(def f1() -> int) | (def f2(name: str) -> int) | (def f3(a: int, b: int) -> int) | (def f4[T: str](x: T@f4) -> int) | Literal[5] | (Overload[() -> None, (x: str) -> str]) | (Overload[() -> None, (x: str, y: str) -> str]) | PossiblyNotCallable`
 info: rule `no-matching-overload` is enabled by default
 
 ```
@@ -176,7 +176,7 @@ info: Function defined here
 8 |     return 0
   |
 info: Union variant `def f2(name: str) -> int` is incompatible with this call site
-info: Attempted to call union type `(def f1() -> int) | (def f2(name: str) -> int) | (def f3(a: int, b: int) -> int) | (def f4(x: T@f4) -> int) | Literal[5] | (Overload[() -> None, (x: str) -> str]) | (Overload[() -> None, (x: str, y: str) -> str]) | PossiblyNotCallable`
+info: Attempted to call union type `(def f1() -> int) | (def f2(name: str) -> int) | (def f3(a: int, b: int) -> int) | (def f4[T: str](x: T@f4) -> int) | Literal[5] | (Overload[() -> None, (x: str) -> str]) | (Overload[() -> None, (x: str, y: str) -> str]) | PossiblyNotCallable`
 info: rule `invalid-argument-type` is enabled by default
 
 ```
@@ -199,8 +199,8 @@ info: Type variable defined here
    |        ^^^^^^
 14 |     return 0
    |
-info: Union variant `def f4(x: T@f4) -> int` is incompatible with this call site
-info: Attempted to call union type `(def f1() -> int) | (def f2(name: str) -> int) | (def f3(a: int, b: int) -> int) | (def f4(x: T@f4) -> int) | Literal[5] | (Overload[() -> None, (x: str) -> str]) | (Overload[() -> None, (x: str, y: str) -> str]) | PossiblyNotCallable`
+info: Union variant `def f4[T: str](x: T@f4) -> int` is incompatible with this call site
+info: Attempted to call union type `(def f1() -> int) | (def f2(name: str) -> int) | (def f3(a: int, b: int) -> int) | (def f4[T: str](x: T@f4) -> int) | Literal[5] | (Overload[() -> None, (x: str) -> str]) | (Overload[() -> None, (x: str, y: str) -> str]) | PossiblyNotCallable`
 info: rule `invalid-argument-type` is enabled by default
 
 ```
@@ -227,7 +227,7 @@ info: Matching overload defined here
 info: Non-matching overloads for function `f5`:
 info:   () -> None
 info: Union variant `Overload[() -> None, (x: str) -> str]` is incompatible with this call site
-info: Attempted to call union type `(def f1() -> int) | (def f2(name: str) -> int) | (def f3(a: int, b: int) -> int) | (def f4(x: T@f4) -> int) | Literal[5] | (Overload[() -> None, (x: str) -> str]) | (Overload[() -> None, (x: str, y: str) -> str]) | PossiblyNotCallable`
+info: Attempted to call union type `(def f1() -> int) | (def f2(name: str) -> int) | (def f3(a: int, b: int) -> int) | (def f4[T: str](x: T@f4) -> int) | Literal[5] | (Overload[() -> None, (x: str) -> str]) | (Overload[() -> None, (x: str, y: str) -> str]) | PossiblyNotCallable`
 info: rule `invalid-argument-type` is enabled by default
 
 ```
@@ -242,7 +242,7 @@ error[too-many-positional-arguments]: Too many positional arguments to function
    |           ^
    |
 info: Union variant `def f1() -> int` is incompatible with this call site
-info: Attempted to call union type `(def f1() -> int) | (def f2(name: str) -> int) | (def f3(a: int, b: int) -> int) | (def f4(x: T@f4) -> int) | Literal[5] | (Overload[() -> None, (x: str) -> str]) | (Overload[() -> None, (x: str, y: str) -> str]) | PossiblyNotCallable`
+info: Attempted to call union type `(def f1() -> int) | (def f2(name: str) -> int) | (def f3(a: int, b: int) -> int) | (def f4[T: str](x: T@f4) -> int) | Literal[5] | (Overload[() -> None, (x: str) -> str]) | (Overload[() -> None, (x: str, y: str) -> str]) | PossiblyNotCallable`
 info: rule `too-many-positional-arguments` is enabled by default
 
 ```