[ty] Meta-type of type variables should be type[..] (#18439)

## Summary

Came across this while debugging some ecosystem changes in
#18347. I think the meta-type of a
typevar-annotated variable should be equal to `type`, not `<class
'object'>`.

## Test Plan

New Markdown tests.

Author: sharkdp

crates/ty_python_semantic/resources/mdtest/generics/pep695/variables.md

@@ -766,4 +766,23 @@ def constrained[T: (Callable[[], int], Callable[[], str])](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
+def normal[T](x: T):
+    reveal_type(type(x))  # revealed: type
+
+def bound_object[T: object](x: T):
+    reveal_type(type(x))  # revealed: type
+
+def bound_int[T: int](x: T):
+    reveal_type(type(x))  # revealed: type[int]
+
+def constrained[T: (int, str)](x: T):
+    reveal_type(type(x))  # revealed: type[int] | type[str]
+```
+
 [pep 695]: https://peps.python.org/pep-0695/

crates/ty_python_semantic/src/types.rs

@@ -5243,7 +5243,7 @@ impl<'db> Type<'db> {
             Type::Tuple(_) => KnownClass::Tuple.to_class_literal(db),
 
             Type::TypeVar(typevar) => match typevar.bound_or_constraints(db) {
-                None => KnownClass::Object.to_class_literal(db),
+                None => KnownClass::Type.to_instance(db),
                 Some(TypeVarBoundOrConstraints::UpperBound(bound)) => bound.to_meta_type(db),
                 Some(TypeVarBoundOrConstraints::Constraints(constraints)) => {
                     // TODO: If we add a proper `OneOf` connector, we should use that here instead