Rollup merge of rust-lang#136355 - GuillaumeGomez:proc-macro_add_value_retrieval_methods, r=Amanieu

Add `*_value` methods to proc_macro lib

This is the implementation of rust-lang/libs-team#459.

It allows to get the actual value (unescaped) of the different string literals.

Part of rust-lang#136652.

r? libs-api

Author: jhpratt

Cargo.lock

@@ -8,6 +8,7 @@ members = [
 ]
 
 exclude = [
+  "literal-escaper",
   # stdarch has its own Cargo workspace
   "stdarch",
   "windows_targets"

Cargo.toml

@@ -0,0 +1,10 @@
+[package]
+name = "literal-escaper"
+version = "0.0.0"
+edition = "2021"
+
+[dependencies]
+std = { version = '1.0.0', optional = true, package = 'rustc-std-workspace-std' }
+
+[features]
+rustc-dep-of-std = ["dep:std"]

literal-escaper/Cargo.toml

@@ -0,0 +1,4 @@
+# literal-escaper
+
+This crate provides code to unescape string literals. It is used by `rustc_lexer`
+and `proc_macro`.