2022-10-31

Auto merge of #13505 - lowr:feat/gats, r=flodiebold

Clean up tests and add documentation for GATs related stuff

This is a follow-up PR for #13494.

- addresses https://github.com/rust-lang/rust-analyzer/pull/13494#discussion_r1006774897
- documents the ordering constraint on `Binders` and `Substitution` (which is not really follow-up for the previous PR, but it was introduced to support GATs and I strongly feel it's worth it)