Auto merge of #24078 - whipsch:extra-token-msg, r=huonw

Addresses issue #22425.  See `src/test/compile-fail/macro-incomplete-parse.rs` for a relevant test:

    macro-incomplete-parse.rs:15:9: 15:10 error: macro expansion ignores token `,` and any following
    macro-incomplete-parse.rs:15         , //~ ERROR macro expansion ignores token `,`
                                         ^
    macro-incomplete-parse.rs:27:1: 27:17 note: caused by the macro expansion here; the usage of `ignored_item` is likely invalid in this context
    macro-incomplete-parse.rs:27 ignored_item!();
                                 ^~~~~~~~~~~~~~~~
    macro-incomplete-parse.rs:20:14: 20:15 error: macro expansion ignores token `,` and any following
    macro-incomplete-parse.rs:20     () => ( 1, 2 ) //~ ERROR macro expansion ignores token `,`
                                              ^
    macro-incomplete-parse.rs:30:5: 30:21 note: caused by the macro expansion here; the usage of `ignored_expr` is likely invalid in this context
    macro-incomplete-parse.rs:30     ignored_expr!();
                                     ^~~~~~~~~~~~~~~~
    macro-incomplete-parse.rs:24:14: 24:15 error: macro expansion ignores token `,` and any following
    macro-incomplete-parse.rs:24     () => ( 1, 2 ) //~ ERROR macro expansion ignores token `,`
                                              ^
    macro-incomplete-parse.rs:32:9: 32:23 note: caused by the macro expansion here; the usage of `ignored_pat` is likely invalid in this context
    macro-incomplete-parse.rs:32         ignored_pat!() => (),
                                         ^~~~~~~~~~~~~~

This does not address the case of improper expansion inside of an impl { } as seen in issue #21607.

I'm not sure if the note text is ideal, but it can be refined if needed.