fix icon-size for small data-driven values

[ansis]

fix #7017, fix #7066

Fixes both issues by scaling icon-size and text-size by 256 instead of 10. It can now represent values from 0 - 256 with precision of 1/256. I think this is enough and saves the bytes compared to using floats.

Launch Checklist

• briefly describe the changes in this PR
• write tests for all new functionality
• document any changes to public APIs
• post benchmark scores
• manually test the debug page
• tagged @mapbox/studio and/or @mapbox/maps-design if this PR includes style spec changes

[ChrisLoer]

This changes makes a lot of sense to me and your implementation looks good. The one thing I'm worried about is text/icon-size overflow. I've seen icon-size overflow at 6554, and now it would overflow at 256. Admittedly, 256 already seems like a big value. In the case I saw a user hitting overflow, they were trying to exponentially size an icon so it matched map scale as you zoomed in. Probably something like a fill layer with a pattern would be a better tool for that particular use case, but when the overflow happens the behavior is really confusing/hard-to-debug. Can we do anything to improve that? Like maybe generate intelligible console errors at expression evaluation time?

[ansis]

93a40f9 adds runtime warnings for icon-size and text-size values that are too big

[ChrisLoer]

👍