Custom fonts + variable fonts

[bdon]

Helper for FontFace API to block drawing until font is loaded

[bdon]

The simplest implementation I can think of is an array of Tasks that is awaited on via Promise.all before every Paint execution.

A task is a promise that resolves when the object is ready to use: A font is loaded into the document, a protosprites sheet has been baked into a canvas, etc.

TODO: figure out what to do when tasks fail/reject. A font or sprite sheet failing to load shouldn't blow up the entire map, or should it?

[bdon]

Map loading will still succeed if individual tasks ,like fonts or sprites, fail to load; how those are handled in failure case is up to the specific task