sort renderable tiles by y and x to match -native

[ansis]

This changes the tile sort order to match -native. This is important to make sure the render order of symbols that cross tile boundaries is the same in -native and -js.

This will let us fix symbol-spacing/line-close for the viewport collision pr in -native.

regressions/mapbox-gl-native#7357/expected.png changes. I think the new rendering is fine, but if we shouldn't change this I can change this so that only symbol rendering order is affected.

Launch Checklist

• briefly describe the changes in this PR
• write tests for all new functionality (built into existing tests and render tests)
• [N/A] document any changes to public APIs
• post benchmark scores https://bl.ocks.org/anonymous/raw/1963f7f03b48d92742d3c17f05ed76d9/
• manually test the debug page

@ChrisLoer

[ChrisLoer]

This looks good to me -- my one concern was that compareKeyZoom ends up getting called pretty heavily, so the more expensive calculation might make a difference. I ran the "paint" and "layout" benchmarks several times and saw this branch as between 53% and 71% likely to be slower than master. I also ran a test on an animated full screen map with the Chrome javascript profiler running and saw getIds taking between .4-1% of CPU time on both branches. So.. seems fine.