fix keeping the wallet unlocked on sw restart after onboarding

[pedronfigueiredo]

Explanation

We want to keep the wallet unlocked when a service worker restarts.

In persistAllKeyrings, when we're building for mv3 and want to cache the encryptionKey but a password was entered and a new encryptionKey has been generated, we want to save encryptionSalt alongside the new encryptionKey in the  keyring controller memStore.

This is so it can be saved in storage and then retrieved on the metamask controller for the extension.

Note that this PR only fixes the first time the service worker is restarted after a fresh wallet is loaded and the onboarding flow is complete. Unlocked wallet persistence for subsequent service worker restarts has been fixed on a separate PR on the extension repository.

For context, this was previously addressed, but the wallet was still locked after a long enough waiting period after the service worker restarted. Another PR has since been merged, making the wallet lock more immediately apparent.

Manual Testing Steps

1. Build the extension wallet from develop

git checkout develop && git pull && yarn && yarn:start:mv3

2. Load the wallet in the browser and complete the onboarding flow

3. Terminate the service worker using chrome://inspect/#service-workers.

4. The wallet should lock after a couple of seconds.

5. Add the changes on index.js on this PR to the corresponding file on the node_modules folder of the Metamask Extension.

6. Build the wallet again.

7. Load the wallet in the browser and complete the onboarding flow

8. Terminate the service worker using chrome://inspect/#service-workers.

9. The wallet should remain unlocked.

Pre-merge author checklist

• I've clearly explained:
  • What problem this PR is solving
  • How this problem was solved
  • How reviewers can test my changes
• Sufficient automated test coverage has been added

Pre-merge reviewer checklist

• Manual testing (e.g. pull and build branch, run in browser, test code being changed)
• PR is linked to the appropriate GitHub issue
• IF this PR fixes a bug in the release milestone, add this PR to the release milestone

If further QA is required (e.g. new feature, complex testing steps, large refactor), add the Extension QA Board label.

In this case, a QA Engineer approval will be be required.

[Gudahtt]

Looks great! Great to have these additional tests, but I think the code being changed here isn't yet adequately covered. I can approve once it's covered by at least one test

[Gudahtt]

LGTM! Left a comment on two tests that can still be improved