Rollup merge of #122120 - fmease:sugg-assoc-ty-bound-on-eq-bound, r=compiler-errors

Suggest associated type bounds on problematic associated equality bounds

Fixes #105056. TL;DR: Suggest `Trait<Ty: Bound>` on `Trait<Ty = Bound>` in Rust >=2021.

~~Blocked on #122055 (stabilization of `associated_type_bounds`), I'd say.~~ (merged)

compiler/rustc_parse/src/errors.rs

@@ -2631,13 +2631,22 @@ pub(crate) struct GenericsInPath {
 }
 
 #[derive(Diagnostic)]
-#[diag(parse_assoc_lifetime)]
+#[diag(parse_lifetime_in_eq_constraint)]
 #[help]
-pub(crate) struct AssocLifetime {
+pub(crate) struct LifetimeInEqConstraint {
     #[primary_span]
-    pub span: Span,
     #[label]
-    pub lifetime: Span,
+    pub span: Span,
+    pub lifetime: Ident,
+    #[label(parse_context_label)]
+    pub binding_label: Span,
+    #[suggestion(
+        parse_colon_sugg,
+        style = "verbose",
+        applicability = "maybe-incorrect",
+        code = ": "
+    )]
+    pub colon_sugg: Span,
 }
 
 #[derive(Diagnostic)]