LibWeb: Update the document cursor position when the selection changes

Otherwise, it looks a bit awkward where the cursor position does not
update while the selection is elsewhere.

Note that this requires passing along the raw selection positions from
`set the selection range` to the elements. Otherwise, consider what will
happen if we set the selection start and end to the same value. By going
through the API accessor, we hit the case where the start and end are
the same value, and return the document cursor position. This would mean
the cursor position would not be updated.

The test changes here more closely match what Firefox produces now. It
is not a 100% match; the `select event fired` test case isn't right. The
problem is the event fires for the input element, but we most recently
focused the textarea element. Thus, when we retrieve the selection from
the input element, we return the document's cursor position, which is
actually in the textarea element. The fix will ultimately be to fully
implement the following:

https://html.spec.whatwg.org/multipage/form-control-infrastructure.html#concept-textarea/input-cursor

That is, each input / textarea element should separately track its own
text cursor position.

Tests/LibWeb/Text/expected/DOM/FormAssociatedElement-selection.txt

@@ -8,7 +8,7 @@ text-input selectionStart: 0 selectionEnd: 18 selectionDirection: none
 text-input selectionStart: 2 selectionEnd: 4 selectionDirection: forward
 text-input selectionStart: 1 selectionEnd: 4 selectionDirection: forward
 text-input selectionStart: 1 selectionEnd: 5 selectionDirection: forward
-text-input selectionStart: 18 selectionEnd: 18 selectionDirection: forward
-text-input selectionStart: 18 selectionEnd: 18 selectionDirection: backward
+text-input selectionStart: 6 selectionEnd: 6 selectionDirection: forward
+text-input selectionStart: 6 selectionEnd: 6 selectionDirection: backward
 textarea selectionStart: 0 selectionEnd: 9 selectionDirection: none
-select event fired: 18 18
+select event fired: 9 9

Userland/Libraries/LibWeb/HTML/FormAssociatedElement.cpp

@@ -541,7 +541,7 @@ void FormAssociatedTextControlElement::set_the_selection_range(Optional<WebIDL::
 
         // AD-HOC: Notify the element that the selection was changed, so it can perform
         //         element-specific updates.
-        selection_was_changed();
+        selection_was_changed(m_selection_start, m_selection_end);
     }
 }
 

Userland/Libraries/LibWeb/HTML/FormAssociatedElement.h

@@ -110,8 +110,6 @@ protected:
     void form_node_was_removed();
     void form_node_attribute_changed(FlyString const&, Optional<String> const&);
 
-    virtual void selection_was_changed() { }
-
 private:
     void reset_form_owner();
 
@@ -159,6 +157,8 @@ protected:
     // https://html.spec.whatwg.org/multipage/form-control-infrastructure.html#concept-textarea/input-relevant-value
     void relevant_value_was_changed(JS::GCPtr<DOM::Text>);
 
+    virtual void selection_was_changed([[maybe_unused]] size_t selection_start, [[maybe_unused]] size_t selection_end) { }
+
 private:
     // https://html.spec.whatwg.org/multipage/form-control-infrastructure.html#concept-textarea/input-selection
     WebIDL::UnsignedLong m_selection_start { 0 };

Userland/Libraries/LibWeb/HTML/HTMLInputElement.cpp

@@ -2362,13 +2362,15 @@ HTMLInputElement::ValueAttributeMode HTMLInputElement::value_attribute_mode() co
     VERIFY_NOT_REACHED();
 }
 
-void HTMLInputElement::selection_was_changed()
+void HTMLInputElement::selection_was_changed(size_t selection_start, size_t selection_end)
 {
+    document().set_cursor_position(DOM::Position::create(realm(), *m_text_node, selection_end));
+
     auto selection = document().get_selection();
     if (!selection || selection->range_count() == 0)
         return;
 
-    MUST(selection->set_base_and_extent(*m_text_node, selection_start().value(), *m_text_node, selection_end().value()));
+    MUST(selection->set_base_and_extent(*m_text_node, selection_start, *m_text_node, selection_end));
 }
 
 }

Userland/Libraries/LibWeb/HTML/HTMLInputElement.h

@@ -206,7 +206,7 @@ public:
     bool selection_or_range_applies() const;
 
 protected:
-    void selection_was_changed() override;
+    void selection_was_changed(size_t selection_start, size_t selection_end) override;
 
 private:
     HTMLInputElement(DOM::Document&, DOM::QualifiedName);

Userland/Libraries/LibWeb/HTML/HTMLTextAreaElement.cpp

@@ -460,13 +460,15 @@ void HTMLTextAreaElement::queue_firing_input_event()
     });
 }
 
-void HTMLTextAreaElement::selection_was_changed()
+void HTMLTextAreaElement::selection_was_changed(size_t selection_start, size_t selection_end)
 {
+    document().set_cursor_position(DOM::Position::create(realm(), *m_text_node, selection_end));
+
     auto selection = document().get_selection();
     if (!selection || selection->range_count() == 0)
         return;
 
-    MUST(selection->set_base_and_extent(*m_text_node, selection_start().value(), *m_text_node, selection_end().value()));
+    MUST(selection->set_base_and_extent(*m_text_node, selection_start, *m_text_node, selection_end));
 }
 
 }

Userland/Libraries/LibWeb/HTML/HTMLTextAreaElement.h

@@ -123,7 +123,7 @@ public:
     void set_dirty_value_flag(Badge<FormAssociatedElement>, bool flag) { m_dirty_value = flag; }
 
 protected:
-    void selection_was_changed() override;
+    void selection_was_changed(size_t selection_start, size_t selection_end) override;
 
 private:
     HTMLTextAreaElement(DOM::Document&, DOM::QualifiedName);