Rollup merge of #127350 - veera-sivarajan:bugfix-126311, r=lcnr

Parser: Suggest Placing the Return Type After Function Parameters

Fixes #126311

This PR suggests placing the return type after the function parameters when it's misplaced after a `where` clause.

This also tangentially improves diagnostics for cases like [this](86d6f1312a/tests/ui/parser/issues/misplaced-return-type-without-where-issue-126311.rs (L1C1-L1C28)) and adds doc comments for `parser::AllowPlus`.

compiler/rustc_parse/src/parser/mod.rs

@@ -495,6 +495,7 @@ impl<'a> Parser<'a> {
             FatalError.raise();
         } else {
             self.expected_one_of_not_found(edible, inedible)
+                .map(|error_guaranteed| Recovered::Yes(error_guaranteed))
         }
     }