Bug 1681483 - Implement persistent storage for QML

[brizental]

See: https://glean-debug-view-dev-237806.firebaseapp.com/pings/brzntl-from-qml

The two pings with that tag were sent from different application runs 🎉

Pull Request checklist

• Quality: Make sure this PR builds and runs cleanly.
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    • npm run test Runs all tests
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• Tests: This PR includes thorough tests or an explanation of why it does not
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[brizental]

Converted to draft because somehow running the QML tests make it so that the WebExt storage tests are not run (and also don't error, thus the green CI).

This PR is ready for review on the QML side though.

[brizental]

Ok, the Storage/WebExt error is not related, and actually might be happening for a while /o\ It is also happening on the events threshold PR.

Filed a bug: https://bugzilla.mozilla.org/show_bug.cgi?id=1717845

[moz-glean]

Build size report

Merging #462 into main will:

• Leave the size of full Web Extension bundle unchanged.
• Increase the size of full Qt/QML bundle build by 4%.

---

	Current size	New size	Size increase
Web Extension
core only	45 KB	45 KB	📈 75 bytes
full bundle	67 KB	67 KB	📈 75 bytes
Qt/QML
core only	104 KB	109 KB	📈 4.4 KB
full bundle	104 KB	109 KB	📈 4.4 KB

[Dexterp37]

r+, the handle thing can be done in a follow-up and reviewed by @badboy if needed.