Implement icon/text-rotate

[mourner]

Implement icon-rotate & text-rotate (specified in degrees).

[ansis]

I think my suggestion to implement this in drawsymbol was wrong. Rotation should probably happen earlier so that the rotated box gets used for collision detection.

mapbox-gl-js/js/text/placement.js

Line 50 in e46712c

if (angle) {

It looks like text-rotate was already implemented, but not as degrees

mapbox-gl-js/js/text/placement.js

Line 83 in e46712c

var rotate = props['text-rotate'];

[mourner]

It seems that it's not that important for icons, because margin of error will be small due to icons being square, and collision detection using axis-parallel bboxes for icons anyway (I wouldn't want to go through full-blown rotation range detection for icons as this would be slow). We can merge now and then fix later.

Also, in the spec, -rotate are not render properties, but class properties, so they can't be processed on the placing step. E.g. they support functions etc.

[ansis]

In the current spec icon-rotate is a class property but text-rotate is a render property. Which should they be? https://github.com/mapbox/mapbox-gl-style-spec/blob/dfad56e1af566ab33927412285b0ab5e3ba79b8b/reference/v4.json#L372

We can merge now and then fix later.

ok