Blender Git Loki

T90371: Asset: Drop Material Tooltip.

This patch changes the drop named material tooltip to give feedback to
the user what is going to happen when they invoke the change.

There are 3 states:
* "": Operator will be canceled as not all data is present (dropping on
background.)
* "Drop <named material> on <object name> (slot <slot number>, replacing
<current material in slot>).
* "Drop <named material> on <object name> (slot <slot number).

Reviewed By: Severin

Maniphest Tasks: T90371

Differential Revision: https://developer.blender.org/D12106