Design Proposal: Add Roll

[NathanMOlson]

Design Proposal: Add Roll

Motivation

I would like to be able to roll the camera (rotate it about the camera boresight).
maplibre/maplibre-gl-js#4717
maplibre/maplibre-gl-js#4780

Proposed Change

I would like to add a field roll to the root style spec object. roll sets the camera roll angle in degrees, and joins its friends pitch and bearing.

API Modifications

Root style spec gets a new roll field. jumpTo(), easeTo(), and flyTo() get roll added to their options. Camera gets a setRoll() method.

Migration Plan and Compatibility

This is a pure extension. To achieve existing functionality, just leave roll undefined (default 0).

Rejected Alternatives

I considered adding roll to the API but not to the style spec. Rejected because:

1. roll is needed in style spec for render tests.
2. Similar fields pitch and bearing already exist in style spec

[HarelM]

I think this can be a good addition.
Feel free to push this forward.
Don't forget the diff part of the implementation here.