[MNT]: mark `**kwargs` as `Any` to suppress warnings about "partially unknown" function signatures in pyright

### Summary

It would be nice if all the `**kwargs` in functions were explicitly marked with `Any` to suppress unknown errors from pyright/pylance in strict mode.

<img width="710" alt="image" src="https://github.com/matplotlib/matplotlib/assets/41439633/819701c6-efa6-4946-80e9-3d877c47536a">


### Proposed fix

replace untyped `**kwargs` with `**kwargs: Any` in function signatures.