Implement 'circle-pitch-alignment' property

[ChrisLoer]

Port from GL JS PR mapbox/mapbox-gl-js#4871.

Fixes issue #9349.

This is my first time using the generate-style-code script. Everything that it spit out looks reasonable, but I'm not sure what extra steps I should take to test the Android/iOS code it generates. I'm not even sure what the auto-generated transition code does.

The one concern I had was that it wanted to interpret anything ending in -alignment as an AlignmentType, which allows an auto value. We don't have an auto value for circle-pitch-alignment, so maybe we should override that with a stricter type? On the other hand, if someone did use auto, the effect would end up being to use the default viewport value, so it wouldn't be a very surprising result.

/cc @jfirebaugh

[jfirebaugh]

How about we allow an auto value as discussed in mapbox/mapbox-gl-js#4871 (taking the value of circle-pitch-alignment), but leave viewport as the default?

[ChrisLoer]

How about we allow an auto value as discussed in mapbox/mapbox-gl-js#4871 (taking the value of circle-pitch-alignment), but leave viewport as the default?

In that discussion scaling was going to be based on alignment. Are you proposing doing it in the opposite direction, with alignment based on the scaling choice? In my mind alignment seems more fundamental than scaling, but I don't know how to justify that position.

[jfirebaugh]

Oh, right. I was thinking of {text,icon}-pitch-alignment, where auto matches -rotation-alignment, which we don't have for circles. So never mind, I agree with you.