fix: earlier onBecome(Un)Observed disposer will not dispose later listener (fix #1537)

[fi3ework]

Thanks for taking the effort to create a PR!

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PR checklist:

• Added unit tests
• Updated changelog
• Updated docs (either in the description of this PR as markdown, or as separate PR on the gh-pages branch. Please refer to this PR). For new functionality, at least API.md should be updated
• Added typescript typings
• Verified that there is no significant performance drop (npm run perf)

This PR is to fix #1537, in become-observed.ts, there is a shared object to store the onBecomeObserved and onBecomeUnobserved for each Atom instance by name. Each Set of the hook of an atom will be initialized only when onBecomeUnobserved or onBecomeUnobserved invoked. So I think there's no harm to the performance.

Looking forward to your opinion 😆

Special thanks to #1771

[mayorovp]

I see two problems on this code:

1. atom names is not guaranteed to be unique;
2. properties on static object atomsObservedListeners are never deleted, so this code is source of memory leaks.

[fi3ework]

@mayorovp Thanks for replying.

1. I think globalState.mobxGuid is just a simple global variable, and only affect by getNextId. Could give me hint why it's not guaranteed.
2. The properties could be deleted when its listeners are removed. This problem could be fixed.

[mayorovp]

User can give any name to atoms manually.

[mayorovp]

3. Who calls orig now? Looks like original handler is forgotten

[fi3ework]

Oh.. It's a fatal mistake I did not realize. Thanks, I' ll try to resolve it.

[fi3ework]

This pr has been rewrote. Welcome review.

[coveralls]

Coverage increased (+0.03%) to 93.605% when pulling 25eb682 on fi3ework:fix-#1537 into d55c50a on mobxjs:master.

[coveralls]

Coverage increased (+0.05%) to 93.623% when pulling 009a482 on fi3ework:fix-#1537 into d55c50a on mobxjs:master.

[fi3ework]

Thanks for reviewing. The pr has updated, there's still an as because I don't know how to infer ${hook}Listeners to be "onBecomeObservedListeners" | "onBecomeUnobservedListeners" gracefully so far 😅

[mweststrate]

Thanks @fi3ework !