LibJS: Rework how native functions are called to improve |this| value

Native functions now only get the Interpreter& as an argument. They can
then extract |this| along with any indexed arguments it wants from it.

This forces functions that want |this| to actually deal with calling
interpreter.this_value().to_object(), and dealing with the possibility
of a non-object |this|.

This is still not great but let's keep massaging it forward.

Libraries/LibJS/Runtime/MathObject.cpp

@@ -32,7 +32,7 @@ namespace JS {
 
 MathObject::MathObject()
 {
-    put_native_function("random", [](Object*, const Vector<Value>&) {
+    put_native_function("random", [](Interpreter&) {
 #ifdef __serenity__
         double r = (double)arc4random() / (double)UINT32_MAX;
 #else