[ty] Infer parameter specializations of generic aliases (#18021)

This updates our function specialization inference to infer type
mappings from parameters that are generic aliases, e.g.:

```py
def f[T](x: list[T]) -> T: ...

reveal_type(f(["a", "b"]))  # revealed: str
```

Though note that we're still inferring the type of list literals as
`list[Unknown]`, so for now we actually need something like the
following in our tests:

```py
def _(x: list[str]):
    reveal_type(f(x))  # revealed: str
```

crates/ty_python_semantic/resources/mdtest/binary/tuples.md

@@ -17,7 +17,6 @@ def _(x: tuple[int, str], y: tuple[None, tuple[int]]):
 
 ```py
 def _(x: tuple[int, ...], y: tuple[str, ...]):
-    # TODO: should be `tuple[int | str, ...]`
-    reveal_type(x + y)  # revealed: tuple[int | Unknown, ...]
+    reveal_type(x + y)  # revealed: tuple[int | str, ...]
     reveal_type(x + (1, 2))  # revealed: tuple[int, ...]
 ```