LibJS: Add the Intl namespace object :^)

This is the start of implementing ECMA-402 in LibJS, better known as the
ECMAScript Internationalization API.

Much like Temporal this gets its own subdirectory (Runtime/Intl/) as
well as a new C++ namespace (JS::Intl) so we don't have to prefix all
the files and classes with "Intl".

https://tc39.es/ecma402/

Userland/Libraries/LibJS/CMakeLists.txt

@@ -72,6 +72,7 @@ set(SOURCES
     Runtime/GlobalEnvironment.cpp
     Runtime/GlobalObject.cpp
     Runtime/IndexedProperties.cpp
+    Runtime/Intl/Intl.cpp
     Runtime/IteratorOperations.cpp
     Runtime/IteratorPrototype.cpp
     Runtime/JSONObject.cpp