Blender Git Loki

VSE: Use lines to draw waveform

Refactor and improve waveform drawing.

Drawing now can use line strips to draw waveforms instead of only
triangle strips. This makes us able to properly visualize thin waveforms
as they would not be visible before. We now also draw the RMS value of
the waveform.

The waveform drawing is now also properly aligned to the screen pixels
to avoid flickering when transforming the strip.

Reviewed By: Richard Antalik

Differential Revision: https://developer.blender.org/D11184