Parse `c"…"` and `cr"…"` string literals

[dtolnay]

RFC: rust-lang/rfcs#3348
Tracking issue: rust-lang/rust#105723

[dtolnay]

Blocked on rust-lang/rust#112820.

[Ddystopia]

Blocker appears to be resolved and c"..." and cr"..." string literals are stabilized in 1.77
cbindgen is not working with this now due to lack of support in syn