Blender Git Loki

Asset Browser: "Make Asset" operator and UI integration

Exposes "Make Asset" in Outliner context menus and button context menus.

The Outliner can tell operators which IDs are selected via a new "selected_ids"
context member. We can use that for more operators and editors in future.
Other UI code can set a new "focused_id" context member (automatically done for
ID pointer property buttons). That way, data-block search menus or other
buttons representing a data-block (e.g. materal slots) can hand an ID to
operators via context.

Differential Revision: https://developer.blender.org/D9717