Merge #11531

11531: fix: Make fill_match_arms assist handle doc(hidden) and non_exhaustive r=Veykril a=OleStrohm

Fixes #11499
Fixes #11500
This keeps track of the relevant attributes and adds in a wildcard pat at the end of the match when necessary.

I decided to do them in the same PR since they both needed the ability to add a wildcard arm, and so their changes would overlap if done separately, but I'll split them up if that seems better.

This is my first PR to rust-analyzer, so all feedback is greatly appreciated!

Co-authored-by: Ole Strohm <[email protected]>

Author: bors[bot]