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/Forward.h

@@ -229,6 +229,7 @@ class AsyncFromSyncIteratorPrototype;
 class AsyncGenerator;
 class AsyncGeneratorPrototype;
 class GeneratorPrototype;
+class WrapForValidIteratorPrototype;
 
 class TypedArrayConstructor;
 class TypedArrayPrototype;