Find a way to DRY up the IOApps

[djspiewak]

Somewhat of a follow up from #4201, though this has been a problem for a long time.

Basically all of the IOApps are very similar (especially JVM and Native), with just a few differences sprinkled throughout, some different documentation, and a few platform-specific APIs. We should try really hard to consolidate the actual code if we can because it's starting to get hard to maintain, especially between JVM and Native.

[kapunga]

Do you mind if I take a crack at this?

[djspiewak]

Go for it! Make sure to double-check mimaReportBinaryIssues, since that's where the trickiness is likely to be (CI will also run this for you, so any PR won't build if bincompat is broken).

[armanbilge]

@kapunga @djspiewak maybe should wait until #4201 is merged, since that changes IOApp on the Native side? Or at least work on that branch?

[kapunga]

I've started working on a draft PR. It's got a ways to go and I'm happy with the approach I'm taking, but if you are super opinionated, you may want to have a look-see.