Fix typo in UDIM operator (always capitalize UI labels)

Cleanup: Fix typo in user preference code

UI: Remove User Preference "Enable All Experimental Features"

Users should be able to know explicitly what they are testing.

By having them all enabled we run into a scenario where a new
experimental feature may have been introduced, and the user
is now using it without being even aware of that.

Differential Revision: https://developer.blender.org/D6404

Fix T71000: Statistics don't take collections hidden state into account

Simple fix, to mimic what we had pre-local collections. So this is not
fully representative of the current load of the scene.

I started a more complex route where we literally just count objects
that are visible (taking object type restriction, local collections,
local view, ...). But in the end it is a bit overkill considering that
we have plans to change the statistics.

Outliner: Fixup for previous commit on tooltip/crash fix

The issue was actually in Python extras (where it shows the ENUM option).

I got a bit distracted by the "(undocumented operator)" message.
It made me miss the missing ENUM once the crash was gone.

Outliner: Fix crash for tooltips on ID operations

This was introduced on 9ca2cbdcea6a.

Outliner: Don't show id operations (make single user) when not supported

For the make single user operation to work we expect a parent of the
datablock to be around. However this is often not the case when not
accessing the data from Scenes or Viewlayer display modes.

For now we simply not show them in the other cases. They can be added
later though, by testing the outliner tree parent compatibility with the
expected parent id.

Fix T71673
Differential Revision: https://developer.blender.org/D6276

Fix T69798: Pinning empty image objects

We have no dedicated image context tab, so for now making sure we don't
end up passing its ID as the pinned one.

If we ever get one, we then will need a different solution here, like
changing the ID that owns the data to be the object, instead of the
empty image datablock.

Differential Revision: https://developer.blender.org/D6273

Merge remote-tracking branch 'origin/blender-v2.81-release'

Fix: Filebrowser saving dialog size when maximized

Reviewed By: Severin

Differential Revision: https://developer.blender.org/D6260