Add Precision "Half" to Compositor Precision options

When creating a styalized/abstract scene, sometimes lower quality settings can produce more exaggerated happy accidents.

But! as of right now, the compositor only previews these effects at "Half" precision and renders it at "Full" (destroying the effect). So Ideally, there should be a third option: "Half" to give a another choice for final rendering precision quality rather than only 1.

Example: