Rollup merge of #42271 - tinaun:charfromstr, r=alexcrichton

add `FromStr` Impl for `char`

fixes #24939.

is it possible to use pub(restricted) instead of using a stability attribute for the internal error representation? is it needed at all?

src/libstd/lib.rs

@@ -254,6 +254,7 @@
 #![feature(cfg_target_thread_local)]
 #![feature(cfg_target_vendor)]
 #![feature(char_escape_debug)]
+#![feature(char_error_internals)]
 #![feature(char_internals)]
 #![feature(collections_range)]
 #![feature(compiler_builtins_lib)]