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

## Summary

Came across this while debugging some ecosystem changes in
https://github.com/astral-sh/ruff/pull/18347. I think the meta-type of a
typevar-annotated variable should be equal to `type`, not `<class
'object'>`.

## Test Plan

New Markdown tests.

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