dev error for excessive pending callbacks

Summary:
We've seen some crashes from exceeding property limits (>200k) from storing callbacks, which is insane since callbacks should be called and cleaned up right away in most cases. Browsing around I never see more than about 50 pending callbacks when firing off a whole much of animations and measures and stuff.

In order to track down the leak, I added some code in `__DEV__` to provide more info - hopefully some developers will hit it and report the issue. Unfortunately it's not easy to get any useful information in prod because we strip all the useful debug info, but if this continues to be a problem we could try capturing that info in prod as well (and maybe other info, too).

Reviewed By: PeteTheHeat

Differential Revision: D16267702

fbshipit-source-id: 8185bb8ff0d646b307c98238616950086b1a608f