These changes will be reverted soon, but to the new implementation

I think this is going to have to come back in JS via canvg or
something. librsvg is too much of a pain (tons of dependencies) and
doesn't integrate with our fonts anyways.

This is too much indirection. Backends have led to a few bugs by
being confusing, and there is zero benefit to such an abstraction.
It's only added LOC and more jumping around files to figure out
what's happening.

IIRC backends were added with the intent to have framebuffer
backends but that never got merged because it's way out of scope.

I broke the JS ctors in ce29f69
so we got lucky and don't have to call this a breaking change.

width * height * approxBytesPerPixel was too big

Zig found via ubsan

the pointer can actually be null in this case which triggers a
ubsan panic