Move entities package from JavaRosa

[seadowg]

Blocked by getodk/javarosa#772

This allows us to iterate on entities without as much back and forth between Collect and JavaRosa changes.

Why is this the best possible solution? Were any other approaches considered?

I could have converted more classes to Kotlin, but there's a lot of code here and I felt like that would easier to review on a case by case basis as we touch those classes.

How does this change affect users? Describe intentional changes to behavior and behavior that could have accidentally been affected by code changes. In other words, what are the regression risks?

A lot of code has been moved, and a few things have been converted to Kotlin, so there's definitely a risk of type conversion problems. The most important things to look at will be form loading and finalization, especially for forms with entities.

Before submitting this PR, please make sure you have:

• added or modified tests for any new or changed behavior
• run ./gradlew connectedAndroidTest (or ./gradlew testLab) and confirmed all checks still pass
• added a comment above any new strings describing it for translators
• added any new strings with date formatting to DateFormatsTest
• verified that any code or assets from external sources are properly credited in comments and/or in the about file.
• verified that any new UI elements use theme colors. UI Components Style guidelines