Document, test, and port (or deprecate) per-layer and per-property transitions

[lucaswoj]

GL JS supports per-property transitions (i.e. circle-color-transition) and per-layer transitions. These features are not documented, tested, or ported to GL Native. We should either

• document, test, and port this feature
• deprecate this feature

cc @mapbox/gl @geohacker

[jfirebaugh]

per-layer transitions

Are you sure about this? As far as I know it supports per-property transitions and a style-wide default. gl-native does as well.

Documentation: mapbox/mapbox-gl-style-spec#171
Testing: mapbox/mapbox-gl-test-suite#116

Deprecation / removal is another alternative. Per-property transitions are not widely used. In fact I'm not aware of any production use.

[lucaswoj]

Are you sure about this?

Nope. A user was complaining that this feature stopped working. I was unaware that we ever supported per-layer transitions but gave them benefit of the doubt.

Seeing as these mapbox/mapbox-gl-style-spec#171 and mapbox/mapbox-gl-test-suite#116 are more actionable, let's focus on those 😄