Create a MainScreenButton theme variation

This turns custom font theme properties into a proper
variation, which makes applying it simpler.

editor/editor_node.cpp

@@ -519,11 +519,6 @@ void EditorNode::_update_theme(bool p_skip_creation) {
 	help_menu->set_item_icon(help_menu->get_item_index(HELP_ABOUT), theme->get_icon(SNAME("Godot"), EditorStringName(EditorIcons)));
 	help_menu->set_item_icon(help_menu->get_item_index(HELP_SUPPORT_GODOT_DEVELOPMENT), theme->get_icon(SNAME("Heart"), EditorStringName(EditorIcons)));
 
-	for (int i = 0; i < main_editor_buttons.size(); i++) {
-		main_editor_buttons.write[i]->add_theme_font_override("font", theme->get_font(SNAME("main_button_font"), EditorStringName(EditorFonts)));
-		main_editor_buttons.write[i]->add_theme_font_size_override("font_size", theme->get_font_size(SNAME("main_button_font_size"), EditorStringName(EditorFonts)));
-	}
-
 	if (EditorDebuggerNode::get_singleton()->is_visible()) {
 		bottom_panel->add_theme_style_override("panel", theme->get_stylebox(SNAME("BottomPanelDebuggerOverride"), EditorStringName(EditorStyles)));
 	}
@@ -3279,21 +3274,21 @@ void EditorNode::add_editor_plugin(EditorPlugin *p_editor, bool p_config_changed
 		Button *tb = memnew(Button);
 		tb->set_flat(true);
 		tb->set_toggle_mode(true);
-		tb->connect("pressed", callable_mp(singleton, &EditorNode::editor_select).bind(singleton->main_editor_buttons.size()));
+		tb->set_theme_type_variation("MainScreenButton");
 		tb->set_name(p_editor->get_name());
 		tb->set_text(p_editor->get_name());
 
 		Ref<Texture2D> icon = p_editor->get_icon();
+		if (icon.is_null() && singleton->theme->has_icon(p_editor->get_name(), EditorStringName(EditorIcons))) {
+			icon = singleton->theme->get_icon(p_editor->get_name(), EditorStringName(EditorIcons));
+		}
 		if (icon.is_valid()) {
 			tb->set_icon(icon);
 			// Make sure the control is updated if the icon is reimported.
 			icon->connect_changed(callable_mp((Control *)tb, &Control::update_minimum_size));
-		} else if (singleton->theme->has_icon(p_editor->get_name(), EditorStringName(EditorIcons))) {
-			tb->set_icon(singleton->theme->get_icon(p_editor->get_name(), EditorStringName(EditorIcons)));
 		}
 
-		tb->add_theme_font_override("font", singleton->theme->get_font(SNAME("main_button_font"), EditorStringName(EditorFonts)));
-		tb->add_theme_font_size_override("font_size", singleton->theme->get_font_size(SNAME("main_button_font_size"), EditorStringName(EditorFonts)));
+		tb->connect("pressed", callable_mp(singleton, &EditorNode::editor_select).bind(singleton->main_editor_buttons.size()));
 
 		singleton->main_editor_buttons.push_back(tb);
 		singleton->main_editor_button_hb->add_child(tb);

editor/themes/editor_fonts.cpp

@@ -390,8 +390,9 @@ void editor_register_fonts(const Ref<Theme> &p_theme) {
 	p_theme->set_font("title", EditorStringName(EditorFonts), bold_fc);
 	p_theme->set_font_size("title_size", EditorStringName(EditorFonts), default_font_size + 1 * EDSCALE);
 
-	p_theme->set_font("main_button_font", EditorStringName(EditorFonts), bold_fc);
-	p_theme->set_font_size("main_button_font_size", EditorStringName(EditorFonts), default_font_size + 1 * EDSCALE);
+	p_theme->set_type_variation("MainScreenButton", "Button");
+	p_theme->set_font("font", "MainScreenButton", bold_fc);
+	p_theme->set_font_size("font_size", "MainScreenButton", default_font_size + 2 * EDSCALE);
 
 	p_theme->set_font("font", "Label", default_fc);