This commit adds to ID struct a new optional 'weak reference' to a
linked ID (in the form of a blend file library path and full ID name).
This can then be used on next append to try to find a matching local ID
instead of re-making the linked data local again.
Ref. T90545
NOTE: ID re-use will be disabled for regular append for the time being
(3.0 release), and only used for assets. Therefore, this commit should
not change anything user-wise.
Differential Revision: https://developer.blender.org/D12545
794c2828af