Python: Ignore await and typing ellipsis as non-effectful statements

[maxfischer2781]

This PR extends the Python StatementNoEffect query to ignore await and many typing ellipses expression statements.

• ignore await expression statements (closes LGTM.com - false positive "Statement has no effect" for Python await #11235)
  • await is used to switch between coroutines and execute long-running effects. While strictly speaking an await can have no side-effect, these are so rare that a purely syntactical analysis seems appropriate.
• ignore ... as the sole expression statement of a typing stub body (closes False positive – "Statement has no effect" for Python type hint ellipsis #11351)
  • @typing.overload indicates a function definition purely for its signature, not implementation. An ... expression statement is commonly used for the body to denote that the body is insignificant.
  • Similar to @typing.overload, a Protocol is only defined for its methods. An ... expression is commonly used for statement bodies.

The Protocol check currently misses generic Protocols (e.g. class Foo(Protocol[T]) and class Bar(Foo[int])). This seems to be a parser bug, see #22298. In principle, the code checks for subscriptions and should be able to pick up such cases once the parser is fixed. To avoid going out of scope here, the parser fixes are in #22301.