Blender Git Loki

Fix (unreported) broken handling of constraints reordering with liboverride.

New drag&drop reordering code would call constraints reordering operator
with the generic context, and not the one from the panel's layout.
missing the "constraint" member which is mandatory for poll function to
properly deal with override vs. local constraints.

This commit fixes it by generating a temp bContextStore in the panel
re-ordering callback.

NOTE: this fix will have to be extended to modifiers (which happen to
work currently because they have an 'active' status), and gpencil
modifiers (which are also broken currently).

Differential Revision: https://developer.blender.org/D13291