Previously, the Annotation panels were a bit buggy in the movie clip editor.
This commit fixes the issue of the panel in the sidebar would disappear
when selecting "Tracks" if no tracks were added to the clip.
To solve this issue the user if given a label text saying "No annotation source"

This commit also removes some grease pencil operators from the toolbar
that do not work with the new annotation system.

This commit also moves the data source choice from the toolbar to the sidebar.
This is needed to migrate the current toolbar to the new tool system
(see T83612)

Some old invalid code was also removed.