cherry-pick from 7241: speed-up matrix44::setconcat when both inputs are scale+translate by inlining the zero-assignments, rather than calling sk_bzero.
cherry-pick from 7241: speed-up matrix44::setconcat when both inputs are
scale+translate by inlining the zero-assignments, rather than calling sk_bzero.

bench: matrix44_setconcat 2x faster



csulmone/skia,csulmone/skia,csulmone/skia,csulmone/skia