The glyph outline blurred, through a mask filter on this pass's own
paint. Not the pass composited and blurred: that is a layer save per
pass, and a different performance story.
This pass with the fields given changed and the rest kept. Every edit
and every rescale goes through here, so a field added to a pass is
carried by all of them rather than dropped by whichever call site
respelled the constructor and forgot it.
This pass painted with paint instead — null included, which is "the
text's own colour" and the one value copyWith cannot say, because
there a null means "not given".