iconBorderRadius for SymbolLayer

Nobody has claimed this yet.

## New Feature

Is there any way to add a border radius to an icon within a `SymbolLayer`, or an equivalent way of rounding the edges and/or make a circular mask on an image from a given url?

The most straightforward use-case for this would be to show circular remote images of locations, users, etc. on the map that are dynamically coming from a remote source and are fully rectangular.

I'm aware that you can modify a `UIImage` to have the desired edge radius before adding it to the map style, however this is fairly cumbersome, and feels like it should be specified at the layer style level instead of the image level. I'm aware that you can achieve a basic circular image on top of the map using a view annotation as well. An alternative implementation could also be to allow an image background in a `CircleLayer`, but this seems fairly restrictive too.


Thanks for the great work so far and congrats on the v11 release!

Start by reading the SymbolLayer image-styling entry point and compare the CircleLayer and view-annotation alternatives mentioned in the issue. Define the supported layer-level behavior and acceptance cases for rounded or circular remote images; the work is done when the chosen API and its rendering behavior are documented and tested.

Written by the indexing model from the issue text.