Rollup merge of #154182 - Unique-Usman:ua/constnotype2, r=estebank

diagnostics: avoid ICE for undeclared generic parameter in impl

Avoid an ICE for:

    struct A;
    impl A<B> {}

The compiler no longer panics and can proceed to emit existing diagnostics.

Adds `tests/ui/missing/undeclared-generic-parameter.rs`.

Fixes rust-lang/rust#154165 and introduced by rust-lang/rust#152913

Author: JonathanBrouwer