Make Onyx values update instantly

[roryabraham]

Coming from: Expensify/App#8306 (comment)

Problem

Setting values in Onyx always takes at least one tick of the event loop and updates subscribers late.

Why this is important

A lot of our code could be made simpler and easier to reason about if we could safely assume that any value written in Onyx will be updated immediately.

Solution

Need to explore a bit, but probably an in-memory cache of some kind. Also need to be careful not to break stuff and to update all our tests appropriately.

[marcaaron]

We have an in memory cache already and force the extra tick because keyChanged() used to happen after a call to AsyncStorage.getItem() (or something like that).

react-native-onyx/lib/Onyx.js

Lines 550 to 551 in 2d42566

	// Optimistically inform subscribers on the next tick
	Promise.resolve().then(() => keyChanged(key, value));

[roryabraham]

I do think this behavior is a bit confusing, but it's not a priority and I'm not going to work on this any time soon. Going to just close this for now