LibWeb: Make HTMLInputElement move cursor into text node when focused

This mechanism feels rather awkward, but it's better than nothing.

Userland/Libraries/LibWeb/DOM/Document.cpp

@@ -894,8 +894,14 @@ void Document::set_focused_element(Element* element)
     if (m_focused_element == element)
         return;
 
+    if (m_focused_element)
+        m_focused_element->did_lose_focus();
+
     m_focused_element = element;
 
+    if (m_focused_element)
+        m_focused_element->did_receive_focus();
+
     if (m_layout_root)
         m_layout_root->set_needs_display();
 }

Userland/Libraries/LibWeb/DOM/Element.h

@@ -132,6 +132,9 @@ public:
 
     virtual RefPtr<Layout::Node> create_layout_node(NonnullRefPtr<CSS::StyleProperties>);
 
+    virtual void did_receive_focus() { }
+    virtual void did_lose_focus() { }
+
 protected:
     virtual void children_changed() override;
 

Userland/Libraries/LibWeb/HTML/HTMLInputElement.cpp

@@ -112,6 +112,21 @@ void HTMLInputElement::create_shadow_tree_if_needed()
     set_shadow_root(move(shadow_root));
 }
 
+void HTMLInputElement::did_receive_focus()
+{
+    auto* browsing_context = document().browsing_context();
+    if (!browsing_context)
+        return;
+    if (!m_text_node)
+        return;
+    browsing_context->set_cursor_position(DOM::Position { *m_text_node, 0 });
+}
+
+bool HTMLInputElement::is_focusable() const
+{
+    return m_text_node;
+}
+
 void HTMLInputElement::inserted()
 {
     HTMLElement::inserted();

Userland/Libraries/LibWeb/HTML/HTMLInputElement.h

@@ -36,6 +36,8 @@ public:
 
     void did_click_button(Badge<Layout::ButtonBox>);
 
+    virtual bool is_focusable() const override;
+
 private:
     // ^DOM::Node
     virtual void inserted() override;
@@ -44,6 +46,9 @@ private:
     // ^HTML::FormAssociatedElement
     virtual HTMLElement& form_associated_element_to_html_element() override { return *this; }
 
+    // ^DOM::EventTarget
+    virtual void did_receive_focus() override;
+
     void create_shadow_tree_if_needed();
 
     RefPtr<DOM::Text> m_text_node;