Rollup merge of #43598 - ibabushkin:master, r=eddyb
Rollup merge of #43598 - ibabushkin:master, r=eddyb

Derive `Hash` on `AssociatedKind`.

This is a trivial change useful in downstream code poking in rustc's
innards, in particular the semver verification tool I'm currently working on.

r? @eddyb

graydon/rust,aidancully/rust,GBGamer/rust,GBGamer/rust,GBGamer/rust,graydon/rust,graydon/rust,graydon/rust,GBGamer/rust,aidancully/rust,GBGamer/rust,aidancully/rust,aidancully/rust,GBGamer/rust,GBGamer/rust,graydon/rust,aidancully/rust,GBGamer/rust,graydon/rust,aidancully/rust