treat `TYPE_CHECKING` blocks the same as stub files

[KotlinIsland]

from typing import TYPE_CHECKING

if TYPE_CHECKING:
    def f(a: int) -> int: ... # whinge whinge, a isn't used

[DetachHead]

it should treat TYPE_CHECKING blocks the same as stub files

[DetachHead]

upstream issues:

• https://github.com/microsoft/pyright/issues/8619#issuecomment-2260735014
• https://github.com/microsoft/pyright/issues/5819