Support initializing map with string JSON style on iOS

[michalgwo]

Is your feature request related to a problem? Please describe.
On Android, we can set style to a map either as a URI or JSON using Style.Builder i.e. Style.Builder().fromJson() or Style.Builder().fromUri(), but on iOS the only option (at least it's the only one I found) is to set styleURL. Setting a style with JSON as a String is useful in my use case when I edit the style in code before initializing a map. The same applies to MapSnapshotter.

Describe the solution you'd like

• Create a new instance property of MLNMapView - styleJSON and/or create the function setStyleJSON.
• Create a new instance property of MLNMapSnapshotOptions - styleJSON

Describe alternatives you've considered
I was thinking about saving a style to a file every time it's edited and then reading it from the file, but it's more a workaround than a real solution. I didn't really explore this option, so I don't even know if it's possible.