This adds an overlay to the animation editors to visualize the current scene strip
in and out points in the scene timeline when the `Sync Scene Time` option in
the sequencer is used.
* Adds an overlay toggle + panel to the dopesheet.
* Adds a new theme setting (for the overlay) under
`Common` > `Animation` > `Scene Strip Range`.
* Adds the overlay drawing to the dopesheet.
Pull Request: https://projects.blender.org/blender/blender/pulls/146165
0c18c1cfc2