UI: sort add-ons by name

Previously add-ons were sorted by category & name, remove the category
only sorting by name since the category is no longer displayed and
isn't part of extension meta-data. Now the add-ons are sorted by name
(case insensitive).

Details:

- Store add-ons modules sorted to avoid having to sort on every redraw.
- addon_utils.modules() now returns an iterator.

tests/python/bl_load_addons.py

@@ -37,9 +37,8 @@ def _init_addon_exclusions():
 
 def addon_modules_sorted():
     # Pass in an empty module cache to prevent `addon_utils` local module cache being manipulated.
-    modules = addon_utils.modules(module_cache={})
-    modules[:] = [
-        mod for mod in modules
+    modules = [
+        mod for mod in addon_utils.modules(module_cache={})
         if not (mod.__file__.startswith(EXCLUDE_DIRECTORIES))
         if not (mod.__name__ in EXCLUDE_ADDONS)
     ]