LibUnicode: Implement grammar validators for Unicode TR-35

ECMA-402 requires validating user input against the EBNF grammar for
Unicode locales described in TR-35: https://www.unicode.org/reports/tr35

This commit adds validators for that grammar, as well as other helper to
e.g. canonicalize a locale string.

Userland/Libraries/LibUnicode/CMakeLists.txt

@@ -3,6 +3,7 @@ include(unicode_data.cmake)
 SET(SOURCES
     ${UNICODE_DATA_SOURCES}
     CharacterTypes.cpp
+    Locale.cpp
 )
 
 serenity_lib(LibUnicode unicode)