Fix bug breaking transparency in fill layers with property functions

[lucaswoj]

This bug is caused by draw_fill's inability to understand property functions when deciding whether to render in the opaque or translucent pass..

To mitigate, this PR draws all fills with property functions for fill-color or fill-opacity in the translucent pass.

fixes #2846

Checklist

• briefly describe the changes in this PR
• write test-suite regression test for this bug
• document any changes or additions to public APIs
• post scores for all benchmarks on your branch and master
• do a quick sanity check on the debug page
• get a PR review 👍 / 👎

[lucaswoj]

Benchmarks

buffer: 938 ms
fps: 60 fps
frame-duration: 6.8 ms, 0% > 16ms
query-point: 0.93 ms
query-box: 48.36 ms
geojson-setdata-small: 10 ms
geojson-setdata-large: 100 ms

master Benchmarks

buffer: 1,013 ms
fps: 60 fps
frame-duration: 6.8 ms, 0% > 16ms
query-point: 0.79 ms
query-box: 44.77 ms
geojson-setdata-small: 10 ms
geojson-setdata-large: 98 ms

[jfirebaugh]

Did this also fix #2827 or #2828?

[lucaswoj]

Yes. I am reasonably confident that both #2827 and #2828 were fixed by this PR.