Isira Seneviratne

> This PR is not just about `SparseArrayCompat`. It contains a lot of other refactorings. Please document them properly in the PR description, otherwise it's difficult to understand why you...

> > Then this PR would raise that requirement to 21, right? Do we want that? > > If I understand correctly, the purpose of this PR is actually to...

@evermind-zz I went through your changes a bit, and they look good to me overall. I've suggested a few changes; for some of these (the Utils encode and decode methods),...

`Base64` support has been [added](https://github.com/google/desugar_jdk_libs/commit/0afb816e1090b754d7d8ad04731cd0ff8424145e) to the desugar library, so we'll be able to remove the uses of `ByteString` from this PR.

> Why do you think `SimplifyOptionalCallChains` is not needed anymore? It was not added by accident: it was added because the IDE was complaining. So why does Android Studio say...

> What are the differences? Why is this an improvement? It removes the need to define the equals and hash code methods separately.

> You may also want to update `com.android.tools:desugar_jdk_libs` to 1.1.8 to target API level 33. (https://github.com/google/desugar_jdk_libs/blob/master/CHANGELOG.md) That's done here: #9285

I improved some of the time difference calculations, e.g. switching from `Duration.between` to `Instant.until`.

I made some changes, this should no longer break existing uses of the methods.

> Have you run the Integration / Android tests on the PR yet? Not yet. I'll run them tomorrow and see if there are any issues.