Add inter-file rules

[ebebbington]

This feature requests stems from the request of a lint rule to not allow (or i guess allow if // ... allow-... is used) async methods that aren't awaited.

Related issues:
#303
#270
#43

But these rely on inter-file rules, which means the checking and grabbing of other files, so we can check if a method is async or not, and only then can we determine if a promise is unhandled.

Though personally, i would have no clue how this would be implemented

[RDambrosio016]

This is impossible without type checking.

[ebebbington]

I should note then, it relies on the roadmap for swc to enable type checking in rust