MDL-82055 output: replace usage of named templatable interface.

It's not available during, and breaks, site installation. The output
class doesn't necessarily need it in 78db6bbce8, so switch to simple
templatable interface instead.

lib/outputcomponents.php

@@ -26,8 +26,7 @@
  * @license http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
  */
 
- use core\output\local\action_menu\subpanel;
- use core\output\named_templatable;
+use core\output\local\action_menu\subpanel;
 
 defined('MOODLE_INTERNAL') || die();
 
@@ -4110,7 +4109,7 @@ class tabobject implements renderable, templatable {
  * @copyright 2015 Adrian Greeve <[email protected]>
  * @license http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
  */
-class context_header implements renderable, named_templatable {
+class context_header implements renderable, templatable {
 
     /**
      * @var string $heading Main heading.
@@ -4232,16 +4231,6 @@ class context_header implements renderable, named_templatable {
             'additionalbuttons' => $additionalbuttons ?? [],
         ];
     }
-
-    /**
-     * Get the template name.
-     *
-     * @param renderer_base $renderer Renderer.
-     * @return string
-     */
-    public function get_template_name(renderer_base $renderer): string {
-        return 'core/contextheader';
-    }
 }
 
 /**

lib/templates/context_header.mustache

@@ -15,7 +15,7 @@
     along with Moodle.  If not, see <http://www.gnu.org/licenses/>.
 }}
 {{!
-    @template core/contextheader
+    @template core/context_header
 
     Context header template.
 

theme/upgrade.txt

@@ -1,12 +1,14 @@
 This files describes API changes in /theme/* themes,
 information provided here is intended especially for theme designer.
 
+=== 4.4.1 ===
+* New `core/context_header` mustache template has been added. This template can be overridden by themes to modify the context header.
+
 === 4.4 ===
 * Theme selection is now performed using cards and modals.
 * The 'choosereadme' string for each theme is expected to be plain text. HTML content will not render when displayed in the modal.
 * Theme selector page has been moved to admin/themeselector.php (previously theme/index.php)
 * Moodleforms no longer use tag 'fieldset' for groups without labels (legends). Avoid targeting tag 'fieldset' in the theme CSS.
-* New `core/contextheader` mustache template has been added. This template can be overridden by themes to modify the context header.
 
 === 4.3 ===
 * The core_renderer::htmllize_file_tree method has been deprecated. This was missed before Moodle 2.0.