Fix F821 false positive for aliased Annotated and Literal imports

[worksbyfriday]

Summary

• Use _is_typing() (scope-aware import resolution) alongside _is_name_or_attr() (literal name check) in the SUBSCRIPT handler for Literal and Annotated
• _is_typing() resolves import aliases through the scope stack, so from typing import Annotated as WithSchema is correctly recognized as a typing member
• The _is_name_or_attr() fallback is preserved to maintain the existing false-negative-safe behavior for non-typing modules that export names called Literal or Annotated
• Added three regression tests for aliased imports

Reproducer

from typing_extensions import Annotated as WithSchema

def f(x: WithSchema[int, "hello"]) -> None:
    return

Before: F821 undefined name 'hello'
After: No warning (metadata arguments in Annotated are correctly treated as non-type expressions)

The same fix applies to Literal aliases.

Closes #789