Reduce complexity of sequencer transform code by removing recursivity.
This is possible by treating meta strips (mostly) as any other strip and
containing all transform code within SEQ_ functions.
Unfortunately internally meta strips still require special treatment,
but all complexity from code all over transform code seems to be
possible to contain within one function.
Functional change:
Previously adjusting handle of single image strip moved animation.
Now animation is not moved, which is behavior for all other strips.
Reviewed By: sergey, mano-wii
Differential Revision: https://developer.blender.org/D11493
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
