scratch-render modified for use in TurboWarp

Changes to upstream:

• faster pen line rendering (by buffering)
• "High Quality Render"/"High Quality Pen" mode

Setup

See https://github.com/TurboWarp/scratch-gui/wiki/Getting-Started to setup the complete TurboWarp environment.

If you just want to play with the render then it's the same process as upstream scratch-render.

API

Compatible with upstream scratch-render.

Renderer.setUseHighQualityRender(boolean) toggles high quality rendering. A UseHighQualityRenderChanged event is emitted on the renderer when this is called.