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Depsgraph: Update armatures when leaving edit mode

The idea is to have proper operation nodes after editing the armature.

This isn't so trivial as it sounds to be, because:

- Dependency graph is being built from the pose channels, which means
adding/deleting bones are not visible to the depsgraph because those
operations doesn't rebuild pose.

- Updating pose after every topology change is rather costy and better
to be avoid.

Currently experimenting with rebuilding dependency graph when leaving
edit mode. This way i can work on partial graph rebuild which would
be really handy for such relations edits.

For now this partial update is rather a place holder and it invokes
full dependency graph rebuild. Actual partial rebuild brains would
be implemented as one of the next steps.

However all this work unleashed rather fundamental questions:

- it is already known that dependency graph uses pose channels for
building.

- Pose channels are being passed to the callback functions as arguments.

- One of operation nodes rebuilds the pose when it's missing or when
it's tagged for update.

- Hrm, ok. Now, what if the pose is tagged for update and some topology
changed? This could change some pose channel pointers leading to the
bad memory access in the callback.

How do we solve this?

- A bit easier question: What should operations do if armature is
edit mode?

Simplest answer would be to copy matricies from bones, skipping
pose rebuild, eval init, pose callbacks and eval flush callbacks.