Auto merge of #47416 - petrochenkov:remove-impl-for-dot-dot, r=petrochenkov

Remove `impl Foo for .. {}` in favor `auto trait Foo {}`

Rebase of https://github.com/rust-lang/rust/pull/46480 with restored parsing support.

diff --cc src/librustc/ty/mod.rs
Simple merge

diff --cc src/libsyntax/feature_gate.rs
Simple merge