Overall the goal of the PR is to show the preview range in the
clip editor's dopesheet and graph mode.
To accomplish this, some cleanup and refactor were needed:
- Clip editor had a nearly 1:1 copy paste of the timeline draw code,
which has been replaced with `ANIM_draw_framerange`.
- Preview range draw code required `bContext`, which was only used to
access scene. Now scene is passed explicitly, without need to know the
context.
- The macro to access the preview range was removed. This is because the
code is within `PRVRANGEON` check, so `PSFRA`/`PEFRA` were doing
redundant checks.
Pull Request: https://projects.blender.org/blender/blender/pulls/138678
24a2da62b3