[WIP] docs: Add documentation for OnyxUpdateManager and deferred updates logic

[chrispader]

@marcaaron @danieldoglas @arosiclair

Explanation of Change

The OnyxUpdateManager is in charge of ensuring data integrity and synchronization of updates received from the backend. This library is quite complicated and complex, especially since we added a new "deferred onyx updates" logic in #38748.

@marcaaron, @danieldoglas, @arosiclair and I discussed and mentioned adding some documentation - and in particular a (flow) diagram - that explains this logic in more detail and makes it easier for developers to understand how we handle (missed) updates and how we persist them in order.

Discussed here:

• Fix: OnyxUpdateManager ends up in a recursive endless loop, when previously applied Onyx updates are not chained (caused crashes on web) #47429 (review)
• Fix: OnyxUpdateManager ends up in a recursive endless loop, when previously applied Onyx updates are not chained (caused crashes on web) #47429 (review)
• Fix: OnyxUpdateManager ends up in a recursive endless loop, when previously applied Onyx updates are not chained (caused crashes on web) #47429 (comment)

I've already added a section under "Philosophy" and created a separate markdown file for the OnyxUpdateManager, which will include more detailed info about implementation, characteristics and usage of the library, as well as a flow diagram similar to the one in the README.md for the data flow.

Fixed Issues

$
PROPOSAL:

Tests

• Verify that no errors appear in the JS console

Offline tests

QA Steps

// TODO: These must be filled out, or the issue title must include "[No QA]."

• Verify that no errors appear in the JS console

PR Author Checklist

• I linked the correct issue in the ### Fixed Issues section above
• I wrote clear testing steps that cover the changes made in this PR
  • I added steps for local testing in the Tests section
  • I added steps for the expected offline behavior in the Offline steps section
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  • Android: mWeb Chrome
  • iOS: Native
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  • MacOS: Desktop
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Screenshots/Videos

Android: Native

Android: mWeb Chrome

iOS: Native

iOS: mWeb Safari

MacOS: Chrome / Safari

MacOS: Desktop