Rollup merge of rust-lang#45101 - lfairy:proc-macro-string-escape, r=jseyfried

Make the result of `Literal::string()` more readable

Closes rust-lang#45076

Author: kennytm

src/libproc_macro/lib.rs

@@ -488,7 +488,7 @@ impl Literal {
     pub fn string(string: &str) -> Literal {
         let mut escaped = String::new();
         for ch in string.chars() {
-            escaped.extend(ch.escape_unicode());
+            escaped.extend(ch.escape_debug());
         }
         Literal(token::Literal(token::Lit::Str_(Symbol::intern(&escaped)), None))
     }