[Tracking] Improvements to Policy.js

[marcaaron]

Problem

Policy.js is a good example of not so great patterns we have created. Let's fix it up so those patterns are not repeated.

Why is this important?

I think we're going to run into similar problems again and again so I wanted to take some time to clean up Policy.js and maybe establish some best practices before people adopt these "less good" ones as a convenience.

Going to break these out into separate issues, but hoping to tackle the following (more info soon).

Solution

Let's create issues for and solve the following:

• Clean up create() and getPolicyList() methods to have single responsibility #6153
• [Discuss] Policies syncing - app unable to sync + modify data in parallel #6081
• inviteUsers() and removeMembers() rely on modifying a copy obtained via Onyx.connect() then calling Onyx.set(). Let's expand Onyx.merge() so it can take a callback instead.

[marcaaron]

Gonna close this for now. Still investigating the need for a better Onyx.merge() in the linked react-native-onyx issue. That other discussion didn't get much traction or land on a solution, but I assume will get dug up again eventually.