fix: Expand literals with wrong suffixes into LitKind::Err

[ShoyuVanilla]

Fixes #20952

For ill-suffixed literals like ""б(Not a number 6 😅), we pass it as fmt_snippet here:

rust-analyzer/crates/hir-def/src/hir/format_args.rs

Line 197 in 00b627d

parse::Parser::new(&text, str_style, fmt_snippet, false, parse::ParseMode::Format);

But in that function the following line panics if the string literal has the suffix ending with a char::len_utf8() > 1
https://doc.rust-lang.org/1.91.0/nightly-rustc/src/rustc_parse_format/lib.rs.html#319

We might limplement some diagnostics or error recovery upon those ill-suffixed string literals but that's not quite doable without some non-trivial refactoring in our parser/token tree/expansion infra. The simplest fix would be just erroring on those literals