Blender Git Loki

VSE: Add strip-time intersection test function

Use SEQ_time_strip_intersects_frame function to test if strip intersects with frame.

Note: There are cases where this function should not be used. For example splitting
strips require at least 1 frame "inside" strip. Another example is drawing, where
playhead technically doesn't intersect strip, but it is rendered, because current
frame has "duration" or "thickness" of 1 frame.

Reviewed By: sergey

Differential Revision: https://developer.blender.org/D11320