PyAPI: postpone loading add-ons until after key-maps have been defined

Loading add-ons after key-maps resolves a problem where add-ons would
setup shortcuts before Blender had created the key-maps.
Making add-ons have to declare the key-maps using region & window types
matching Blender's internal values.

This PR a pitfall pointed out in #110030.

Ref !110092

scripts/modules/bpy/utils/__init__.py

@@ -189,7 +189,7 @@ _global_loaded_modules = []  # store loaded module names for reloading.
 import bpy_types as _bpy_types  # keep for comparisons, never ever reload this.
 
 
-def load_scripts(*, reload_scripts=False, refresh_scripts=False):
+def load_scripts(*, reload_scripts=False, refresh_scripts=False, extensions=True):
     """
     Load scripts and run each modules register function.
 
@@ -199,6 +199,8 @@ def load_scripts(*, reload_scripts=False, refresh_scripts=False):
     :arg refresh_scripts: only load scripts which are not already loaded
        as modules.
     :type refresh_scripts: bool
+    :arg: extensions: Loads additional scripts (add-ons & app-templates).
+    :type: extensions: bool
     """
     use_time = use_class_register_check = _bpy.app.debug_python
     use_user = not _is_factory_startup
@@ -306,21 +308,8 @@ def load_scripts(*, reload_scripts=False, refresh_scripts=False):
                         for mod in modules_from_path(path, loaded_modules):
                             test_register(mod)
 
-    # load template (if set)
-    if any(_bpy.utils.app_template_paths()):
-        import bl_app_template_utils
-        bl_app_template_utils.reset(reload_scripts=reload_scripts)
-        del bl_app_template_utils
-
-    # Deal with add-ons separately.
-    _initialize_once = getattr(_addon_utils, "_initialize_once", None)
-    if _initialize_once is not None:
-        # First time, use fast-path.
-        _initialize_once()
-        del _addon_utils._initialize_once
-    else:
-        _addon_utils.reset_all(reload_scripts=reload_scripts)
-    del _initialize_once
+    if extensions:
+        load_scripts_extensions(reload_scripts=reload_scripts)
 
     if reload_scripts:
         _bpy.context.window_manager.tag_script_reload()
@@ -342,6 +331,31 @@ def load_scripts(*, reload_scripts=False, refresh_scripts=False):
                         )
 
 
+def load_scripts_extensions(*, reload_scripts=False):
+    """
+    Load extensions scripts (add-ons and app-templates)
+
+    :arg reload_scripts: Causes all scripts to have their unregister method
+       called before loading.
+    :type reload_scripts: bool
+    """
+    # load template (if set)
+    if any(_bpy.utils.app_template_paths()):
+        import bl_app_template_utils
+        bl_app_template_utils.reset(reload_scripts=reload_scripts)
+        del bl_app_template_utils
+
+    # deal with addons separately
+    _initialize = getattr(_addon_utils, "_initialize", None)
+    if _initialize is not None:
+        # first time, use fast-path
+        _initialize()
+        del _addon_utils._initialize
+    else:
+        _addon_utils.reset_all(reload_scripts=reload_scripts)
+    del _initialize
+
+
 def script_path_user():
     """returns the env var and falls back to home dir or None"""
     path = _user_resource('SCRIPTS')