Apply clamp_to_embedder on parent resize and popup.

Fixes #75084.

The clamp_to_embedder setting was added in 8be16e0704873f0c9bab8c10dafe2607a00ff78f,
but was not set on any of the in-editor dialogs.

This patch sets `clamp_to_embedder` on editor dialogs so they cannot be dragged out of the frame.
This also modifies `clamp_to_embedder` so a window is clamped to the bounds of an embedder when
it pops up and when the parent is resized.

editor/project_settings_editor.cpp

@@ -582,6 +582,7 @@ void ProjectSettingsEditor::_bind_methods() {
 ProjectSettingsEditor::ProjectSettingsEditor(EditorData *p_data) {
 	singleton = this;
 	set_title(TTR("Project Settings (project.godot)"));
+	set_clamp_to_embedder(true);
 
 	ps = ProjectSettings::get_singleton();
 	data = p_data;