COLRv1 bounds computation traverses unnecessary branches

[drott]

In COLRv1 bounds computation, clients of Skrifa would usually use a call to ColorGlyph::paint with a ColorPainter that tracks the bounds of the pushed operations.

However, branches / parts of the glyph below the first clip level do not need to be tracked further, as the bounds cannot grow after an initial clip.

Clients can track this and ignore operations after the initial clip level.

But to address this inefficiency and not issue the extra calls, we could for example add a mode for the ColorPainter object so it can be asked whether it is in bounds mode - or a switch to the paint()method, or perform bounds computation in Skrifa (but this might be tricky due to handling client side transforms?).