Stop worrying about tiny OOMs. Work towards #20449.
While going through these, I also changed the function signature in many
places where returning ThrowCompletionOr<T> is no longer necessary.
This is a first pass at implementing CRC2D.createPattern() and the
associated CanvasPattern object. This implementation only works for a
few of the required image sources [like CRC2D.drawImage()], and does
not yet support transforms. Other than that it supports everything
else (which is mainly the various repeat modes).
