9cade06f5f
Replace `bNodeInstanceHash` with a `Map`. Move it to the node tree runtime data. Simplify some code by removing the tag from the hash value and collecting unused previews directly. Then just remove a bunch of code that's now unused. Note that texture node previews haven't been working for a while anyway, and the experimental shader node previews seem to use a different system (this one is a remnant of Blender Internal). Pull Request: https://projects.blender.org/blender/blender/pulls/135310