Summary: public
Add RCTFatal for reporting fatal runtime conditions. This centralizes failure handling to one function and allows you to customize how they should be handled. RCTFatal will be logged to the console and as a redbox and will also be triggered by fatal exceptions coming from RCTExceptionsManager.
Note that there is no RCTLogFatal, since just logging the fatal condition does not allow us to handle it consistently.
Reviewed By: nicklockwood
Differential Revision: D2615490
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