Extensions: split add-ons & extensions into separate preferences

Add back the "Add-ons" preferences, removing add-on logic from
extensions.

- Add support for filtering add-ons by tags
  (separate from extension tags).
- Tags now respect the "Only Enabled" option.
- Remove the ability to enable/disable add-ons from extensions.
- Remove add-on preferences from extensions.
- Remove "Legacy" & "Core" prefix from add-on names.
- Remove "Show Legacy Add-ons" filtering option.

Implements design task #122735.

Details:

- Add-on names and descriptions are no longer translated,
  since it's impractical to translate text which is mostly
  maintained outside of Blender.
- Extensions names have a `[disabled]` suffix when disabled so it's
  possible to identify installed but disabled extensions.
- The add-on "type" is shown in the details,
  so it's possible to tell the difference between an extension,
  a core add-on & a legacy user add-on.
- Icons are also used to differentiate the add-on type.
- User add-on's must be uninstalled from the add-ons section
  (matching 4.1 behavior).
- Simplify logic for filtering tags, move into a function.

source/blender/makesdna/DNA_userdef_types.h

@@ -1142,7 +1142,7 @@ typedef enum eUserPref_Section {
   USER_SECTION_SYSTEM = 3,
   USER_SECTION_THEME = 4,
   USER_SECTION_INPUT = 5,
-  USER_SECTION_EXTENSIONS = 6,
+  USER_SECTION_ADDONS = 6,
   USER_SECTION_LIGHT = 7,
   USER_SECTION_KEYMAP = 8,
 #ifdef WITH_USERDEF_WORKSPACES
@@ -1155,6 +1155,7 @@ typedef enum eUserPref_Section {
   USER_SECTION_NAVIGATION = 14,
   USER_SECTION_FILE_PATHS = 15,
   USER_SECTION_EXPERIMENTAL = 16,
+  USER_SECTION_EXTENSIONS = 17,
 } eUserPref_Section;
 
 /** #UserDef_SpaceData.flag (State of the user preferences UI). */

source/blender/makesrna/intern/rna_userdef.cc

@@ -60,6 +60,7 @@ const EnumPropertyItem rna_enum_preference_section_items[] = {
     {USER_SECTION_ANIMATION, "ANIMATION", 0, "Animation", ""},
     RNA_ENUM_ITEM_SEPR,
     {USER_SECTION_EXTENSIONS, "EXTENSIONS", 0, "Extensions", ""},
+    {USER_SECTION_ADDONS, "ADDONS", 0, "Add-ons", ""},
     {USER_SECTION_THEME, "THEMES", 0, "Themes", ""},
 #if 0 /* def WITH_USERDEF_WORKSPACES */
     RNA_ENUM_ITEM_SEPR,