Data block list

[Durman]

Addressed problem description

closes #3873

Welcome suggestions if any

Preflight checklist

• Code changes complete.
• Code documentation complete.
• Documentation for users complete.
• Manual testing done.
• Ready for merge.

[Durman]

The problem of the Object socket is that it keeps straight reference to a data block which can become invalid in any moment. We have quite a few input nodes with such socket this is probably why it's not big problem now. It looks like that Blender devs did something and calling method of such objects doesn't cause a crash as it was before. Now it rises the references error.

2021-02-25.14-12-23.mp4

Solution could be instead of keeping straight references to keep meta information for searching a data block. Obvious disadvantage of this is that the search will take O(len(data block collection)) each time. To make it more efficient will be tricky task. Probably, a socket ,before sv_get method, should check whether reference to an object is valid and if not search the data block in appropriate collection.