[android] Add a method to make map snapshots

[vkurchatkin]

Fixes: #3466

/cc @tobrun

TODO list:

• - add tests (need some guidance);
• - maybe move API to MapboxMap instead;
• - docs.

[tobrun]

@vkurchatkin this is really awesome, will review soon!

[tobrun]

maybe move the API to MaboxMap instead

I haven't reviewed the code or compiled the PR, but here already some feedback:

This would improve our parity with Google so having that in MapboxMap would make more sense.

add support for reusing a bitmap

Google maps supports 2 methods for taking a snapshot:

• public final void snapshot (GoogleMap.SnapshotReadyCallback callback)
• public final void snapshot (GoogleMap.SnapshotReadyCallback callback, Bitmap bitmap)

Ideally we also support both where the latter can reuse bitmaps for performance reasons.

add tests (need some guidance);

Hit me up with any questions you have on this. Related to this feature, it will be hard to write proper unit tests for this but we should be able to come up with some integration/ui tests.

[vkurchatkin]

Google maps supports 2 methods for taking a snapshot

Somehow missed it, makes sense

[tobrun]

I'm going to pull this in to our repo to run the CI tests, this will also allow me to rebase the commits.
Thanks again for the contribution!

Update you can follow in #4564

[vkurchatkin]

@tobrun Thanks!