Add semantic token modifier to imported modules

[zhouzq-thu]

Feature request:

Add a modifier to the classes and functions tokens those imported from other modules.

I think it will be very useful to distinguish the current file from other modules.

I'd like to assign the new semantic token type to "*.library" as the standard modifier like C++ and rust.

Situation

#561 add "builtin" modifier to the Python built-in functions.