With the move to the new snapping system,
the snapping flags were no longer stored on the editor but on the scene.
While that is good for all editors that deal with animation,
it also affected the Driver Editor since that is effectively a Graph Editor.
However since the driver editor doesn't deal with frames,
it is unlikely that settings should be shared with other animation editors.
With this PR the Driver Editor gets it's own snapping flag,
which means snapping can be controlled without affecting
other animation editors.
This also removes snapping options
* Snap to markers doesn't make sense, there are no markers in drivers
* Snap to seconds also makes no sense
Only snap to frames, i.e. whole numbers is kept with the option
to snap directly to whole numbers or offset the current position
by a whole number.
Pull Request: https://projects.blender.org/blender/blender/pulls/136826
d2f1b6570d