Auto merge of #116124 - WaffleLapkin:fix-proc-macro-literal-to-string, r=compiler-errors

Properly print cstr literals in `proc_macro::Literal::to_string`

Previously we printed the contents of the string, rather than the actual string literal (e.g. `the c string` instead of `c"the c string"`).

Fixes #112820
cc #105723

Author: bors