Addresses a PR comment by mcdurdin on #13597 (at https://github.com/keymanapp/keyman/pull/13597#discussion_r2023971170) in regard to the motivation for gesture input serialization.
> I just don't understand how the problem described here can arise -- unless we are introducing deferral with promises -- but even then, if we consistently defer every incoming event with a promise, then the order would still be automatically enforced.
In particular, this aims to clarify how the macrotask queue gets involved and can interfere with the ordering of promises.