Lex lifetimes using emoji and emit appropriate error

[estebank]

Lex and parse emoji in lifetimes, and disallow them in the parser with a hard error. Allow emoji to start a lifetime name even if they are not XID_Start.

error: lifetimes cannot contain emoji
  --> $DIR/emoji-in-lifetime.rs:1:22
   |
LL | fn bad_lifetime_name<'🐛🐛🐛family👨👩👧👦>(
   |                      ^^^^^^^^^^^^^^^^^^^^^

Address #141081 (but we could provide more information in the diagnostic, pointing at the specific chars, providing a link to the reference on identifiers and/or some other extra information).

[rustbot]

The parser was modified, potentially altering the grammar of (stable) Rust
which would be a breaking change.

cc @fmease

[rustbot]

r? @jdonszelmann

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[rust-log-analyzer]

The job pr-check-2 failed! Check out the build log: (web) (plain enhanced) (plain)

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    |                 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ missing field `has_emoji`
    |
help: include the missing field in the pattern
    |
258 |                 rustc_lexer::TokenKind::Lifetime { starts_with_number, has_emoji } => {
    |                                                                      +++++++++++
help: if you don't care about this missing field, you can explicitly ignore it
    |
258 |                 rustc_lexer::TokenKind::Lifetime { starts_with_number, has_emoji: _ } => {
    |                                                                      ++++++++++++++
help: or always ignore missing fields here
    |
258 |                 rustc_lexer::TokenKind::Lifetime { starts_with_number, .. } => {
    |                                                                      ++++