0a0a5a956c
Properly handle emojis as literal prefix in macros
Do not accept the following
```rust
macro_rules! lexes {($($_:tt)*) => {}}
lexes!(🐛"foo");
```
Before, invalid emoji identifiers were gated during parsing instead of lexing in all cases, but this didn't account for macro pre-expansion of literal prefixes.
Fix #123696.