Blender Git Loki

Assets: Expose option to reuse data-block data when appending

With 794c2828af60 & f48a4aa0f915 it's possible to reuse possibly
expensive, nested data of a data-block when appending. E.g. the
texture of a material, or the mesh of an object. Without this it's easy
to bloat memory and the file size. Duplicated textures also cause
unnecessary shader recompilations.

The feature was intended to be the new default behavior for the Asset
Browser, but it wasn't actually added to the UI yet. This patch adds a
new import type option to the Asset Browser. So from the menu in the
header, you can now choose between:

* Link
* Append
* Append (Reuse Data)

The latter is the new default.

Maniphest Task: https://developer.blender.org/T91741

Differential Revision: https://developer.blender.org/D12647

Reviewed by: Sybren St�vel, Bastien Montagne