fix: incorrect error message for string literal suffixes

[notJoon]

Description

Fixes #144161

When a raw string literal has an invalid suffix (like r#"test"#suffix), the compiler was not reporting the appropriate error message "suffixes on string literals are invalid". This was particularly problematic when the suffix was immediately followed by another token, as in r#" \\ "#r"\\ ".

Changes

Modified parse_expr_lit to handle raw string literals with suffixes by:

1. Checking if a token is a raw string literal with a suffix before general literal parsing
2. Using the existing LitKind::from_token_lit to validate and get the appropriate error

To prevent cascading errors, consume the next token if it's another string literal after an error is reported.

[rustbot]

r? @petrochenkov

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[petrochenkov]

This is incorrect, the string literal suffix is a semantic error, not a parsing error, and this code

#[cfg(false)]
fn check() {
    let _ = r#"raw"#suffix;
}

should compile successfully.

@rustbot author

[rustbot]

Reminder, once the PR becomes ready for a review, use @rustbot ready.

[bors]

☔ The latest upstream changes (presumably #144689) made this pull request unmergeable. Please resolve the merge conflicts.