LibJS: Implement Iterator.from and the WrapForValidIteratorPrototype

Iterator.from creates an Iterator from either an existing iterator or
an iterator-like object. In the latter case, it sets the prototype of
the returned iterator to WrapForValidIteratorPrototype to wrap around
the iterator-like object's iteration methods.

Userland/Libraries/LibJS/CMakeLists.txt

@@ -257,6 +257,7 @@ set(SOURCES
     Runtime/WeakSet.cpp
     Runtime/WeakSetConstructor.cpp
     Runtime/WeakSetPrototype.cpp
+    Runtime/WrapForValidIteratorPrototype.cpp
     Runtime/WrappedFunction.cpp
     Script.cpp
     SourceCode.cpp