fixes #5810: post animateCamera()/easeCamera() callbacks on main thread

[incanus]

Naive approach here based on my experience, but I think that it's correct. Please tell me it really is this simple!

/cc @bleege @zugaldia @cammace @ivovandongen

[ivovandongen]

@incanus Let's discuss this first on Monday. There is more to this than reported in #5810 as I described and am working on in #5721.

[incanus]

Sounds good—figured, as with threading issues almost all of the time, that it's more complex than first blush.

[ivovandongen]

@incanus There's actually more going on still. Just created an activity to re-create the issue and ran into a stack overflow exception. I'm going to make a separate ticket for that as well so we can discuss the root cause.

[incanus]

After offline discussion with @bleege @ivovandongen, broader context here is that with rendering on the main thread now, this shouldn't be an issue as such and this PR is irrelevant. We may still yet have race condition issues around state and clearing internal cyclical callbacks, e.g. #5836, but something like what is proposed here purely in Java land does not need to be happening.