Auto merge of #72080 - matthewjasper:uniform-impl-trait, r=nikomatsakis

Clean up type alias impl trait implementation

- Removes special case for top-level impl trait
- Removes associated opaque types
- Forbid lifetime elision in let position impl trait. This is consistent with the behavior for inferred types.
- Handle lifetimes in type alias impl trait more uniformly with other parameters

cc #69323
cc #63063
Closes #57188
Closes #62988
Closes #69136
Closes #73061

diff --cc src/librustc_ast/ast.rs
Simple merge

diff --cc src/librustc_hir/hir.rs
Simple merge

diff --cc src/librustc_hir/intravisit.rs
Simple merge

diff --cc src/librustc_hir_pretty/lib.rs
Simple merge

diff --cc src/librustc_lint/builtin.rs
Simple merge

diff --cc src/librustc_privacy/lib.rs
Simple merge

diff --cc src/librustc_save_analysis/dump_visitor.rs
Simple merge

diff --cc src/librustc_save_analysis/lib.rs
Simple merge

diff --cc src/librustc_typeck/check/coercion.rs
Simple merge

diff --cc src/librustc_typeck/check/mod.rs
Simple merge

diff --cc src/tools/clippy/clippy_lints/src/utils/hir_utils.rs
Simple merge

diff --cc src/tools/clippy/clippy_lints/src/utils/inspector.rs
Simple merge