LibWeb: Fix "incorrect behavior on select()"

This patch resolves the problem outlined in issue LadybirdBrowser#1446, where the
cursor_position node could be substituted with any other existing
node by the mousedown event. Previously, if this new node was not
equal to m_text_node, the function would return prematurely without
updating the selection.

With this fix, we ensure that the selection is properly updated in
such cases, rather than simply exiting the function.

Also, in order to address the issue in LadybirdBrowser#1339, the logic of
document().set_cursor_position has been put behind to the logic of
Selection.

Closes LadybirdBrowser#1446

Userland/Libraries/LibWeb/HTML/HTMLInputElement.cpp

@@ -2429,13 +2429,14 @@ HTMLInputElement::ValueAttributeMode HTMLInputElement::value_attribute_mode() co
 
 void HTMLInputElement::selection_was_changed(size_t selection_start, size_t selection_end)
 {
-    if (!m_text_node || !document().cursor_position() || document().cursor_position()->node() != m_text_node)
+    if (!m_text_node)
         return;
 
-    document().set_cursor_position(DOM::Position::create(realm(), *m_text_node, selection_end));
-
     if (auto selection = document().get_selection())
         MUST(selection->set_base_and_extent(*m_text_node, selection_start, *m_text_node, selection_end));
+
+    if (document().cursor_position() && document().cursor_position()->node() == m_text_node)
+        document().set_cursor_position(DOM::Position::create(realm(), *m_text_node, selection_end));
 }
 
 }

Userland/Libraries/LibWeb/HTML/HTMLTextAreaElement.cpp

@@ -461,13 +461,14 @@ void HTMLTextAreaElement::queue_firing_input_event()
 
 void HTMLTextAreaElement::selection_was_changed(size_t selection_start, size_t selection_end)
 {
-    if (!m_text_node || !document().cursor_position() || document().cursor_position()->node() != m_text_node)
+    if (!m_text_node)
         return;
 
-    document().set_cursor_position(DOM::Position::create(realm(), *m_text_node, selection_end));
-
     if (auto selection = document().get_selection())
         MUST(selection->set_base_and_extent(*m_text_node, selection_start, *m_text_node, selection_end));
+
+    if (document().cursor_position() && document().cursor_position()->node() == m_text_node)
+        document().set_cursor_position(DOM::Position::create(realm(), *m_text_node, selection_end));
 }
 
 }