Signed-off-by: cui fliter <imcusg@gmail.com>

Fix rust-lang#80476.

Fix misuses of a vs an

Fixes the misuse of "a" vs "an", according to English grammatical
expectations and using https://www.a-or-an.com/

…estebank

More accurately point to where default return type should go

When getting the "default return type" span, instead of pointing to the low span of the next token, point to the high span of the previous token. This:

1. Makes forming return type suggestions more uniform, since we expect them all in the same place.
2. Arguably makes labels easier to understand, since we're pointing to where the implicit `-> ()` would've gone, rather than the starting brace or the semicolon.

r? ```@estebank```

…, r=compiler-errors

Diagnostics: Be more careful when suggesting struct fields

Consolidate the various places which filter out struct fields that shouldn't be suggested into a single function.

Previously, each of those code paths had slightly different and incomplete metrics for no good reason. Now, there's only a single 'complete' metric (namely `is_field_suggestable`) which also filters out hygienic fields that come from different syntax contexts.

Fixes rust-lang#116334.

…rrors

Tweak wording of E0562

Fix rust-lang#80476.

rustdoc: rename `issue-\d+.rs` tests to have meaningful names (part 2)

Follow up rust-lang#116214