Add support for a new method on executor future which terminates a chain and executes its callback regardless of failures to schedule. The intention is for this function to allow for cleanup that always needs to occur.

An ideal signature would look like:

void getAsyncMaybeInline(StatusOrStatusWith<T> t, bool executorShutdown)

the extra parameter would allow the caller to identify when they might be running inline, and to possibly take extra precaution in that case