Icon collision boxes don't account for icon-text-fit

[ChrisLoer]

See discussion at #5632.

CollisionFeature takes a Shaping as an input for determining the size of collision boxes. This works fine for text, but for icons with icon-text-fit: true, the quads generated for the icon by getIconQuads may not match the Shaping.

I suspect the right fix here is to move most of the icon-text-fit logic into shapeIcon.

My guess is this hasn't been a big deal in practice because when people are using icon-text-fit they also use icon-allow-overlap and icon-ignore-placement, and rely on the matching text's collision box. But it'd be better not to have that gotcha.

/cc @jfirebaugh @ansis @anandthakker

[kkaefer]

This will be fixed by #8741