Display loading text while the project manager is loading

This hints the user that the project manager is currently busy
loading the project. This is important for the HTML5 editor as the
current feedback isn't very obvious.

This also removes the unused `_exit_dialog` function.

editor/project_manager.cpp

@@ -2040,6 +2040,10 @@ void ProjectManager::_global_menu_action(const Variant &p_id, const Variant &p_m
 
 void ProjectManager::_open_selected_projects() {
 
+	// Show loading text to tell the user that the project manager is busy loading.
+	// This is especially important for the HTML5 project manager.
+	loading_label->set_modulate(Color(1, 1, 1));
+
 	const Set<String> &selected_list = _project_list->get_selected_project_keys();
 
 	for (const Set<String>::Element *E = selected_list.front(); E; E = E->next()) {
@@ -2312,12 +2316,6 @@ void ProjectManager::_restart_confirm() {
 	get_tree()->quit();
 }
 
-void ProjectManager::_exit_dialog() {
-
-	_dim_window();
-	get_tree()->quit();
-}
-
 void ProjectManager::_install_project(const String &p_zip_path, const String &p_title) {
 
 	npdialog->set_mode(ProjectDialog::MODE_INSTALL);
@@ -2407,7 +2405,6 @@ void ProjectManager::_bind_methods() {
 	ClassDB::bind_method("_erase_missing_projects_confirm", &ProjectManager::_erase_missing_projects_confirm);
 	ClassDB::bind_method("_language_selected", &ProjectManager::_language_selected);
 	ClassDB::bind_method("_restart_confirm", &ProjectManager::_restart_confirm);
-	ClassDB::bind_method("_exit_dialog", &ProjectManager::_exit_dialog);
 	ClassDB::bind_method("_on_order_option_changed", &ProjectManager::_on_order_option_changed);
 	ClassDB::bind_method("_on_filter_option_changed", &ProjectManager::_on_filter_option_changed);
 	ClassDB::bind_method("_on_projects_updated", &ProjectManager::_on_projects_updated);
@@ -2537,6 +2534,13 @@ ProjectManager::ProjectManager() {
 	search_tree_vb->set_h_size_flags(SIZE_EXPAND_FILL);
 
 	HBoxContainer *sort_filters = memnew(HBoxContainer);
+	loading_label = memnew(Label(TTR("Loading, please wait...")));
+	loading_label->add_font_override("font", get_font("bold", "EditorFonts"));
+	loading_label->set_h_size_flags(Control::SIZE_EXPAND_FILL);
+	sort_filters->add_child(loading_label);
+	// Hide the label but make it still take up space. This prevents reflows when showing the label.
+	loading_label->set_modulate(Color(0, 0, 0, 0));
+
 	Label *sort_label = memnew(Label);
 	sort_label->set_text(TTR("Sort:"));
 	sort_filters->add_child(sort_label);
@@ -2555,8 +2559,6 @@ ProjectManager::ProjectManager() {
 	int projects_sorting_order = (int)EditorSettings::get_singleton()->get("project_manager/sorting_order");
 	project_order_filter->set_filter_option((ProjectListFilter::FilterOption)projects_sorting_order);
 
-	sort_filters->add_spacer(true);
-
 	project_filter = memnew(ProjectListFilter);
 	project_filter->add_search_box();
 	project_filter->connect("filter_changed", this, "_on_filter_option_changed");

editor/project_manager.h

@@ -56,6 +56,7 @@ class ProjectManager : public Control {
 
 	ProjectListFilter *project_filter;
 	ProjectListFilter *project_order_filter;
+	Label *loading_label;
 
 	FileDialog *scan_dir;
 	ConfirmationDialog *language_restart_ask;