The Annotations panel does not work in the Sequencer(strip area) or in Backdrop preview mode, and is not supposed to, so it only should be exposed in the Sequencer Preview and Sequencer/Preview modes(T66112). Also, old deprecated Grease Pencil code also needs to be renamed and/or removed from the space_sequencer.py (T67331)
So, this patch fixes these elements:
- Limit exposing the Annotation panel to view modes: Sequencer Preview and Sequencer/Preview, since the Annotations do not work in the other view modes.
- Removing SEQUENCER_PT_grease_pencil_tools, since it is old deprecated code, and the panel was not exposed in the UI.
- Renaming SEQUENCER_PT_grease_pencil to SEQUENCER_PT_annotation, since this is the 2.80 naming.
NB. the Annotations panel in the Sequencer(strip area) is not included in the 2.80 manual, and this fix will not cause an update of the manual.