[ty] Add meta-type tests for legavy TypeVars (#18453)

## Summary

Follow up to the comment by @dcreager
[here](#18439 (comment)).

Author: sharkdp

crates/ty_python_semantic/resources/mdtest/generics/legacy/variables.md

@@ -196,4 +196,33 @@ def constrained(f: T):
     reveal_type(f())  # revealed: int | str
 ```
 
+## Meta-type
+
+The meta-type of a typevar is the same as the meta-type of the upper bound, or the union of the
+meta-types of the constraints:
+
+```py
+from typing import TypeVar
+
+T_normal = TypeVar("T_normal")
+
+def normal(x: T_normal):
+    reveal_type(type(x))  # revealed: type
+
+T_bound_object = TypeVar("T_bound_object", bound=object)
+
+def bound_object(x: T_bound_object):
+    reveal_type(type(x))  # revealed: type
+
+T_bound_int = TypeVar("T_bound_int", bound=int)
+
+def bound_int(x: T_bound_int):
+    reveal_type(type(x))  # revealed: type[int]
+
+T_constrained = TypeVar("T_constrained", int, str)
+
+def constrained(x: T_constrained):
+    reveal_type(type(x))  # revealed: type[int] | type[str]
+```
+
 [generics]: https://typing.python.org/en/latest/spec/generics.html