[ty] Support typing.TypeAliasType (#18156)

## Summary

Support direct uses of `typing.TypeAliasType`, as in:

```py
from typing import TypeAliasType

IntOrStr = TypeAliasType("IntOrStr", int | str)

def f(x: IntOrStr) -> None:
    reveal_type(x)  # revealed: int | str
```

closes https://github.com/astral-sh/ty/issues/392

## Ecosystem

The new false positive here:
```diff
+ error[invalid-type-form] altair/utils/core.py:49:53: The first argument to `Callable` must be either a list of types, ParamSpec, Concatenate, or `...`
```
comes from the fact that we infer the second argument as a type
expression now. We silence false positives for PEP695 `ParamSpec`s, but
not for `P = ParamSpec("P")` inside `Callable[P, ...]`.

## Test Plan

New Markdown tests

crates/ty_project/tests/check.rs

@@ -294,4 +294,8 @@ impl SourceOrderVisitor<'_> for PullTypesVisitor<'_> {
 
 /// Whether or not the .py/.pyi version of this file is expected to fail
 #[rustfmt::skip]
-const KNOWN_FAILURES: &[(&str, bool, bool)] = &[];
+const KNOWN_FAILURES: &[(&str, bool, bool)] = &[
+    // Fails with too-many-cycle-iterations due to a self-referential
+    // type alias, see https://github.com/astral-sh/ty/issues/256
+    ("crates/ruff_linter/resources/test/fixtures/pyflakes/F401_34.py", true, true),
+];