Mark many things as internal

[williamito]

Description Mark many things as internal, as they don't seem to be used by any public API. This will significantly streamline generated documentation.

Type Code Health

Screenshots (if applicable)

Checklist

• [x] I have read and acknowledged the Code of conduct.
• [x] I have read the Contributing page.
• [x] I have signed the Google Individual CLA, or I am covered by my company's Corporate CLA.
• [ ] I have discussed my proposed solution with code owners in the linked issue(s) and we have agreed upon the general approach.
• [x] I have run ./gradlew spotlessApply and ./gradlew spotlessCheck to check my code follows the style guide of this project.
• [x] I have run ./gradlew check and ./gradlew connectedCheck to test my changes locally.
• [ ] I have built and run the demo app(s) to verify my change fixes the issue and/or does not break the demo app(s).

[williamito]

Switching to draft, I'm finding a lot of other things that appear to be safely marked internal

[santosh-pingle]

@santosh-pingle can you run the demo app and just check that the db is functioning as expected (don't need to spend too much time)

@aditya-07 in case you spot anything wrong here.

thanks @williamito this is fine by me as long as tests pass - nothing glaringly wrong to me.

After this pull request was updated with the latest code changes (PR#2497), the upload sync was working fine, and the database was not throwing any exceptions.

[jingtang10]

thanks so much santosh for testing!