generator: Emit new `c""` `CStr` literals

[MarijnS95]

These ~will land in Rust 1.76~ have landed in Rust 1.77 just now and automatically append a \0 terminator in the compiler without having to have a checked or unsafe-unchecked constructor on CStr.

Hacking in an invalid \0 anywhere in the string is disallowed with a compiler error.

Note that proc-macro, and by extension proc-macro2 only has support for parsing this literal, but not for emitting it yet.

[Friz64]

C-string literals have now landed in Rust 1.77.