LibHTML: Make hit testing work for LayoutText

LayoutText can't simply rely on its LayoutNode::rect() for hit testing.
Instead, we have to iterate over the individual runs and see if we're
hitting any of them.

Also, LayoutNode::hit_test() now always recurses into children, since
we can't trust the rect() to tell the truth (inline rects are wrong.)

Libraries/LibHTML/Layout/LayoutText.h

@@ -26,7 +26,12 @@ public:
 
     const Vector<Run>& runs() const { return m_runs; }
 
+    virtual HitTestResult hit_test(const Point&) const override;
+
 private:
+    template<typename Callback>
+    void for_each_run(Callback) const;
+
     void load_font();
     void compute_runs();