fix: Fix dependency tracking and useSES bug

[shuding]

Fixes #2446. CC @promer94.

The overall idea of useSES is that state changes are triggered from the external. It works in a pipeline of "external state change → compare it with local state's snapshot → trigger re-render and update local state". The main catch here is that SWR's dependency tracking system (stateDependencies.data = true) isn't considered as a state in that loop. But then, even if we put stateDependencies part of the state and compare/update it through useSES, we can't do a synchronous read of the snapshot which is required as we use a getter:

get data() {
  // Trigger a re-render synchronously with the updated snapshot
  setCache({ stateDependencies_data: true })

  return returnData
},

Mentally this should work (similar to this example) but it doesn't seem to with useSES.

So in this PR, an extra ref latestComparedState is added to track the latest snapshot that useSES received inside, and return that state if possible. This shouldn't cause any problem in concurrent rendering because the process should happen in the same component instance and tick as useSES's returned state, but as a complete state.

This way we are still managing the state via useSES but only re-renders it when necessary.

Here's a diagram explaining the idea:

codesandbox ci

https://codesandbox.io/s/2446-grkt00?file=/src/App.js
https://codesandbox.io/s/swr-re-render-dn2whh?file=/src/App.tsx

[codesandbox-ci]

This pull request is automatically built and testable in CodeSandbox.

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Latest deployment of this branch, based on commit 9cf2713:

Sandbox	Source
SWR-Basic	Configuration
SWR-States	Configuration
SWR-Infinite	Configuration
SWR-SSR	Configuration
#2446	PR
swr re-render	PR

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📊 Modified Dependency Overview:

⬆️ Updated Package	Version Diff	Added Capability Access	+/- Transitive Count	Publisher
@types/react@18.0.38	18.0.27...18.0.38	None	+0/-0	types

[promer94]

I'm not sure why there's a failing test case

The test is failing due to changes in the implementation of isEqual, resulting in more calls to compare than in the previous version. We just need to update the snapshots

[promer94]

The most difficult part of this bug is that when the value of stateDependencies.data changes, returnData has actually been calculated through getSnapshot.

Alternatively, I think that we can modify the implementation of getSnapshot.

By updating the value of memorizedSnapshot but not modifying its reference, we can ensure that the value returned by useSES is always synchronized with the cache and won't cause any unnecessary rerenders.