LibWeb: Clip overflowing inline children when overflow != "visible"

We now apply a paint-time clip to the padding rect of a BlockBox before
painting its inline-level children. This covers some of the behavior
we want from "overflow: hidden" etc but is far from a complete solution.

Userland/Libraries/LibWeb/Layout/BlockBox.h

@@ -55,6 +55,8 @@ public:
 
 private:
     virtual bool is_block_box() const final { return true; }
+
+    bool should_clip_overflow() const;
 };
 
 template<>