Extensions: Install From Disk operator handling both legacy and new

When a user has downloaded an add-on as a zip file, it's not clear in
advance if this is a legacy add-on or a new extension. So they would
have to use trial and error, or inspect the zip file contents.

This uses a simple heuristic to check if the file is a legacy add-on,
and if so automatically calls the legacy operator instead.

The operator now show both extension and legacy add-on properties,
with the latter in a default collapsed subpanel.

Pull Request: https://projects.blender.org/blender/blender/pulls/121926

scripts/modules/rna_manual_reference.py

@@ -3214,6 +3214,7 @@ url_manual_mapping = (
     ("bpy.ops.object.shade_flat*", "scene_layout/object/editing/shading.html#bpy-ops-object-shade-flat"),
     ("bpy.ops.paintcurve.select*", "sculpt_paint/brush/stroke.html#bpy-ops-paintcurve-select"),
     ("bpy.ops.pose.paths_update*", "animation/motion_paths.html#bpy-ops-pose-paths-update"),
+    ("bpy.ops.preferences.addon_install*", "advanced/extensions/addons.html#bpy-ops-preferences-addon-install"),
     ("bpy.ops.preferences.addon*", "editors/preferences/addons.html#bpy-ops-preferences-addon"),
     ("bpy.ops.scene.light_cache*", "render/eevee/render_settings/indirect_lighting.html#bpy-ops-scene-light-cache"),
     ("bpy.ops.screen.actionzone*", "interface/window_system/areas.html#bpy-ops-screen-actionzone"),