[MOV] website_forum: split templates per main usage

PURPOSE

Reorganize website_forum module. This allows to better locate code, understand
organization, and prepare future changes.

SPECIFICATIONS

Split templates by main usage. Files have been duplicated previously, they
are now cleaned to keep only content relevant to their usage. Split is done
according to

  * base file: layouts for main actions not specifically managed in other
    sub-files: display a forum, manage tags, post a new question or edit
    a question;
  * '_forum_all': 'all' page in multi-forum display, displaying the list of
    available forum;
  * '_layout': layouting templates. Modifications to global layout and forum
    specific page header used through all main templates;
  * '_moderation': moderation tools;
  * '_post': display a forum post;
  * '_tools': tooling and utility blocks, used as black boxes in various
    main templates;

Task-3240082 (Forum: Reorganize and lint module)

Part-of: odoo/odoo#114841

addons/website_forum/__manifest__.py

@@ -33,8 +33,14 @@ Ask questions, get answers, no distractions
         'views/res_users_views.xml',
         'views/gamification_karma_tracking_views.xml',
         'views/forum_menus.xml',
+
         'views/base_contact_templates.xml',
         'views/forum_forum_templates.xml',
+        'views/forum_forum_templates_forum_all.xml',
+        'views/forum_forum_templates_layout.xml',
+        'views/forum_forum_templates_moderation.xml',
+        'views/forum_forum_templates_post.xml',
+        'views/forum_forum_templates_tools.xml',
         'views/website_profile_templates.xml',
         'views/snippets/snippets.xml',