When drawing a text frame with a mask blur, we currently just apply a gaussian blur to the rendered text. This renders the correct result when the color source is a solid color (for example, while drawing shadows), but if the color source is something else, we'll end up erroneously blurring the color source and not just the mask.

When addressing this, we need to be careful about how mask blurs interact with color filters, lest we wind up color filtering content unmodulated by the geometry mask of the text.