[ty] support kw_only=True for dataclass() and field() (#19677)

## Summary
https://github.com/astral-sh/ty/issues/111

adds support for `@dataclass(kw_only=True)`
(https://docs.python.org/3/library/dataclasses.html)

## Test Plan
- new mdtests
- triaged conformance diffs (notes here:
https://diffswarm.dev/d-01k2gknwyq82f6x17zqf3apjxc)
- `mypy_primer` no-op

crates/ty_python_semantic/resources/mdtest/dataclasses/dataclass_transform.md

@@ -195,7 +195,41 @@ OrderTrueOverwritten(1) < OrderTrueOverwritten(2)
 
 ### `kw_only_default`
 
-To do
+When provided, sets the default value for the `kw_only` parameter of `field()`.
+
+```py
+from typing import dataclass_transform
+from dataclasses import field
+
+@dataclass_transform(kw_only_default=True)
+def create_model(*, init=True): ...
+@create_model()
+class A:
+    name: str
+
+a = A(name="Harry")
+# error: [missing-argument]
+# error: [too-many-positional-arguments]
+a = A("Harry")
+```
+
+TODO: This can be overridden by the call to the decorator function.
+
+```py
+from typing import dataclass_transform
+
+@dataclass_transform(kw_only_default=True)
+def create_model(*, kw_only: bool = True): ...
+@create_model(kw_only=False)
+class CustomerModel:
+    id: int
+    name: str
+
+# TODO: Should not emit errors
+# error: [missing-argument]
+# error: [too-many-positional-arguments]
+c = CustomerModel(1, "Harry")
+```
 
 ### `field_specifiers`
 

crates/ty_python_semantic/resources/mdtest/dataclasses/dataclasses.md

@@ -465,7 +465,84 @@ To do
 
 ### `kw_only`
 
-To do
+An error is emitted if a dataclass is defined with `kw_only=True` and positional arguments are
+passed to the constructor.
+
+```toml
+[environment]
+python-version = "3.10"
+```
+
+```py
+from dataclasses import dataclass
+
+@dataclass(kw_only=True)
+class A:
+    x: int
+    y: int
+
+# error: [missing-argument] "No arguments provided for required parameters `x`, `y`"
+# error: [too-many-positional-arguments] "Too many positional arguments: expected 0, got 2"
+a = A(1, 2)
+a = A(x=1, y=2)
+```
+
+The class-level parameter can be overridden per-field.
+
+```py
+from dataclasses import dataclass, field
+
+@dataclass(kw_only=True)
+class A:
+    a: str = field(kw_only=False)
+    b: int = 0
+
+A("hi")
+```
+
+If some fields are `kw_only`, they should appear after all positional fields in the `__init__`
+signature.
+
+```py
+@dataclass
+class A:
+    b: int = field(kw_only=True, default=3)
+    a: str
+
+A("hi")
+```
+
+The field-level `kw_only` value takes precedence over the `KW_ONLY` pseudo-type.
+
+```py
+from dataclasses import field, dataclass, KW_ONLY
+
+@dataclass
+class C:
+    _: KW_ONLY
+    x: int = field(kw_only=False)
+
+C(x=1)
+C(1)
+```
+
+### `kw_only` - Python < 3.10
+
+For Python < 3.10, `kw_only` is not supported.
+
+```toml
+[environment]
+python-version = "3.9"
+```
+
+```py
+from dataclasses import dataclass
+
+@dataclass(kw_only=True)  # TODO: Emit a diagnostic here
+class A:
+    x: int
+    y: int
+```
 
 ### `slots`
 

crates/ty_python_semantic/resources/mdtest/dataclasses/fields.md

@@ -63,13 +63,12 @@ class Person:
     age: int | None = field(default=None, kw_only=True)
     role: str = field(default="user", kw_only=True)
 
-# TODO: the `age` and `role` fields should be keyword-only
-# revealed: (self: Person, name: str, age: int | None = None, role: str = Literal["user"]) -> None
+# revealed: (self: Person, name: str, *, age: int | None = None, role: str = Literal["user"]) -> None
 reveal_type(Person.__init__)
 
 alice = Person(role="admin", name="Alice")
 
-# TODO: this should be an error
+# error: [too-many-positional-arguments] "Too many positional arguments: expected 1, got 2"
 bob = Person("Bob", 30)
 ```