Initial implementation of f-curve drawing for the video sequencer.
The patch adds a flag in the VSE's View menu //(active by default)// for drawing opacity and volume f-curves as darker regions of the strips.
A similar solution could also be used for the NLA editor's influence curves. //(currently drawn as gray lines)//.
{F8419663}
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To get better performance:
* Only the visible sections of the curve //(inside the editor borders)// are evaluated.
* The amount of frames for which the curve is evaluated depends on the zoom level.
Further performance improvements could probably be achieved in curve lookups.