Previously only attributes of "real" geometry were displayed in
attribute search. This commit adds code to look through attributes
on instances and add those to the search drop-down too.
This required implementing the same sort of recursive traversal as
the realize instances code. The situation is a bit different though,
this can return early and doesn't need to keep track of transforms.
I added a limit so that it doesn't look through the attributes of
too many instanced geometry sets. I think this is important, since
this isn't a trivial operation and it could potentially happen for
every node in a large node tree. Currently the limit is set at 8
geometry sets, which I expect will be enough, since the set of
attributes is mostly not very unique anyway.
Fixes T86282
Diffrential Revision: https://developer.blender.org/D10919
1ec9ac2016