MapSnapshotter using style json

[tobrun]

A blocker for getting our render node test suite running on Android in #10047, is the ability to create a MapSnapshot using a local style json. A render test consists out of a style.json and the resulting expected.png (see an example here). Atm a snapshot can only load a style from a styleUrl. Suggesting to implement this as MapSnapshotter.Options#setStyleJson.