[core] Enable circle-sort-key property

[ahk]

Adds support for circle-sort-key property, consistent with symbol-sort-key.

Sorts drawing order by sort key both within-tile and cross-tile.

Fixes: #15008

[chloekraw]

@ahk #15839 has landed -- should we rebase this pr against master and then get it reviewed?

[pozdnyakov]

@ahk the approach looks nice! 👍 I'll be able to give more thorough review after the rebase and once CI is passing (pls tell if I could help with that).

[ahk]

once CI is passing (pls tell if I could help with that).

Hey @pozdnyakov, rebase was no problem but I've spent a bit of time (unsuccessfully) trying to figure out why my PR doesn't pass CI. Anything stand out to you?

I know the code formatting check is also failing but really the troubling thing is the segfault in the test runner on for example next-linux-clang8-release. It happens during mbgl::gl::Program<mbgl::CircleProgram>::draw() when attempting mbgl::gl::value::VertexAttribute::Set.

[1ec5]

Also remove these lines from the Darwin version of this script:

mapbox-gl-native/platform/darwin/scripts/generate-style-code.js

Lines 18 to 19 in 1f266b4

	// FIXME: https://github.com/mapbox/mapbox-gl-native/issues/15008
	delete spec.layout_circle["circle-sort-key"]

[1ec5]

In the future, these properties should be deleted in scripts/style-spec.js instead of both scripts/generate-style-code.js and platform/darwin/scripts/generate-style-code.js. This is the reason for the layout of indirection in scripts/style-spec.js.

[1ec5]

Now that most of platform/darwin/ has been deleted in favor of the sources in the mapbox/mapbox-gl-native-ios repository, mapbox/mapbox-gl-native-ios#272 will take care of deleting the remnants of this override.

[pozdnyakov]

🚢