Don't display "Fill segment" option if editable mapping is active

[dieknolle3333]

URL of deployed dev instance (used for testing):

• https://disablefillsegmentwithactiveeditablemapping.webknossos.xyz/
• e.g. DS ROI2017_wkw_sparse_segmentation (I think it only has JSON mappings, not sure where a HDF5 mapping can be found to reproduce the bug)

How to test

• create editable mapping and make sure that flood filling is not available in the context menu any more
• advanced: change code so that it is available in context menu again, and click is while editable mapping is active. there should be a toast and a console.error.
• in an annotation with a segmentation layer, turn it invisible and turn on a skeleton layer. now only skeleton options should be available in the context menu in the viewport, matching the disabled volume actions in the action bar.

TODOs:

• disable flood filling if there is no active segmentation layer
• see if disabledVolumeInfo can be used even more
• DRY nonSkeletonActions

Issues:

• fixes Fill Segment can be triggered while an editable mapping is active #7925

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(Please delete unneeded items, merge only when none are left open)

• Updated changelog
• Removed dev-only changes like prints and application.conf edits

[philippotto]

great :) only see my one comment.