Copy WTF-8 code into core/alloc (for better diffs)
diff --git a/library/std/src/sys_common/wtf8.rs b/library/alloc/src/wtf8/mod.rs
similarity index 100%
copy from library/std/src/sys_common/wtf8.rs
copy to library/alloc/src/wtf8/mod.rs
diff --git a/library/std/src/sys_common/wtf8/tests.rs b/library/alloc/src/wtf8/tests.rs
similarity index 100%
rename from library/std/src/sys_common/wtf8/tests.rs
rename to library/alloc/src/wtf8/tests.rs
diff --git a/library/std/src/sys_common/wtf8.rs b/library/core/src/wtf8.rs
similarity index 100%
rename from library/std/src/sys_common/wtf8.rs
rename to library/core/src/wtf8.rs