Fix #143699: Pose library asset shelf does not apply poses

This was quite involved to get to work. Basic idea is to make
`bl_activate_operator` work for the pose library asset shelf, and
introducing a `bl_drag_operator` for blending poses.

- Make pose asset operators take an asset reference, which is how
  `bl_activate_operator` usually gets the asset to operate on. This way
  poses references can be assigned to a shortcut, identified by asset
  library and relative asset path within the library. Falls back to
  getting the asset from context.
- Trigger `bl_activate_operator` on every click, instead of only when
  an un-active item becomes active. Needed so poses can be re-applied
  as before.
- Fix button context not passed to the `bl_activate_operator` when
  force-activating, e.g. on right-click events.
- Allow registering a `bl_drag_operator` in the asset shelf definition.
  Executed when dragging an asset in the shelf.
- When dragging an asset, highlight it as active, without calling the
  `bl_activate_operator`. This is important feedback to the user.
- Activate/select view items on click instead of drag, so dragging is
  possible.
- Let pose applying operators handle the Ctrl key to apply poses
  flipped. There's no simple way to attach such alternative behaviors
  to `bl_activate_operator`/`bl_drag_operator`
- Remove keymap items that were there for the previous "hacky" solution
  to apply & blend poses.

Pull Request: https://projects.blender.org/blender/blender/pulls/144023

scripts/presets/keyconfig/keymap_data/blender_default.py

@@ -1042,7 +1042,7 @@ def km_user_interface(_params):
         ("ui.view_scroll", {"type": 'WHEELUPMOUSE', "value": 'ANY'}, None),
         ("ui.view_scroll", {"type": 'WHEELDOWNMOUSE', "value": 'ANY'}, None),
         ("ui.view_scroll", {"type": 'TRACKPADPAN', "value": 'ANY'}, None),
-        ("ui.view_item_select", {"type": 'LEFTMOUSE', "value": 'PRESS'}, None),
+        ("ui.view_item_select", {"type": 'LEFTMOUSE', "value": 'CLICK'}, None),
         ("ui.view_item_select", {"type": 'LEFTMOUSE', "value": 'PRESS', "ctrl": True},
          {"properties": [("extend", True)]}),
         ("ui.view_item_select", {"type": 'LEFTMOUSE', "value": 'PRESS', "shift": True},

scripts/presets/keyconfig/keymap_data/industry_compatible_data.py

@@ -420,7 +420,7 @@ def km_user_interface(params):
         ("anim.driver_button_remove", {"type": 'D', "value": 'PRESS', "alt": True}, None),
         ("anim.keyingset_button_add", {"type": 'K', "value": 'PRESS'}, None),
         ("anim.keyingset_button_remove", {"type": 'K', "value": 'PRESS', "alt": True}, None),
-        ("ui.view_item_select", {"type": 'LEFTMOUSE', "value": 'PRESS'}, None),
+        ("ui.view_item_select", {"type": 'LEFTMOUSE', "value": 'CLICK'}, None),
     ])
 
     return keymap