Support multiple columns in select widgets

[grzesiek2010]

Closes #426

I realized that now as we use RecyclerView it's easy to solve this issue and give our users a new option.

What has been done to verify that this works as intended?

I used the attached form for testing and confirmed that it works as expected.

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

I'm not sure if the appearance columns-n I used is the best approach but it's easy to change. I was thinking about compact-n but it's already used to create GridWidgets so it would cause conflicts.

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?

I can't see any risk here it should be safe and shouldn't change anything else.

Do we need any specific form for testing your changes? If so, please attach one.

columns.zip

Does this change require updates to documentation? If so, please file an issue here and include the link below.

Before submitting this PR, please make sure you have:

• run ./gradlew checkAll and confirmed all checks still pass OR confirm CircleCI build passes and run ./gradlew connectedDebugAndroidTest locally.
• 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

[lognaturel]

Good to know the implementation is now straightforward!

Not sure if you saw this before but there's ongoing discussion at XLSForm/xlsform.github.io#125 and https://forum.opendatakit.org/t/spec-proposal-harmonize-compact-compact-n-horizontal-horizontal-compact-appearances/15565 so I'm going to close for now until we can write out exactly what the appearances should be and how they should combine.

Definitely keep the implementation around.