LibWeb+LibJS: Add a naive way to check if a wrapper "is" a certain type

Instead of only checking the class_name(), we now generate an is_foo()
virtual in the wrapper generator. (It's currently something we override
on Bindings::Wrapper, which is not really scalable.)

Longer term we'll need to think up something smarter for verifying that
one wrapper "is" another type of wrapper.

Libraries/LibJS/Runtime/Object.h

@@ -111,6 +111,8 @@ public:
     virtual bool is_symbol_object() const { return false; }
     virtual bool is_bigint_object() const { return false; }
 
+    virtual bool is_web_wrapper() const { return false; }
+
     virtual const char* class_name() const override { return "Object"; }
     virtual void visit_children(Cell::Visitor&) override;