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Depsgraph: support depending on collection geometry

This fixes T87666 and T83252.

The boolean modifier and geometry nodes can depend on the geometry
of an entire collection. Before, the modifiers had to manually create relations
to all the objects in the collection. This worked for the most part, but was
cumbersome and did not solve all issues. For example, the modifiers were not
properly updated when objects were added/removed from the referenced collection.

This commit introduces the concept of "collection geometry" in the depsgraph.
The geometry of a collection depends on the transforms and geometry of all
the objects in it. The boolean modifier and geometry nodes can now just depend
on the collection geometry instead of creating all the dependencies themselves.

Differential Revision: https://developer.blender.org/D11053