RFC 0463 Future-proof literal suffixes

RFC 0463 (rust-lang/rfcs#0463, which was before Rust 1.0) decided that at lexing time quoted literals and numeric literals can include arbitrary suffixes, not just those suffixes that are currently accepted in literal expressions.

The form of the suffix is the same as the form of an identifier-or-keyword. A lone underscore isn't allowed as the suffix for a quoted literal (for a numeric literal such an underscore would be allowed, but treated as part of the final sequence of digits not as a suffix).

The FLS currently describes the situation before that RFC, where the only suffixes allowed at lexing time were the type indicators.

That is, the FLS is incorrectly saying that a MacroInvocation like m!("abc"d) would be treated as seeing two tokens "abc" and d, when in fact there's only one.

(In 2021 when the FLS was written that Reference was in a similar state to the FLS, but it has been updated since.)

Read the FLS rules for lexing quoted and numeric literals, then compare them with RFC 0463 and the updated Rust Reference. Update the FLS so arbitrary identifier-or-keyword suffixes are handled correctly, including the m!("abc"d) MacroInvocation example, and verify the resulting tokenization description.