Auto merge of #126161 - Bryanskiy:delegation-generics-4, r=petrochenkov

Delegation: support generics in associated delegation items

This is a continuation of rust-lang/rust#125929.

[design](https://github.com/Bryanskiy/posts/blob/master/delegation%20in%20generic%20contexts.md)

Generic parameters inheritance was implemented in all contexts. Generic arguments are not yet supported.

r? `@petrochenkov`

Author: bors