Explained the need to support database downgrading

[grzesiek2010]

Closes #6315

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

We have discussed the issue and agreed that since downgrading is not officially supported we should stop handling it in our codebase.

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?

Downgrading isn't officially supported, so we don't typically test for it. I believe we can skip testing in this case as well. A code review by @seadowg.

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

No.

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

No.

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

[seadowg]

Thanks for looking into this! Seeing this, I'm actually leaning towards the oppositive and just exploding if we get a call to onDowngrade. I think the idea that data gets cleared out might be more dangerous than just crashing and letting the user export the data if they still need it or at least understand that they're in a bad state. Would be good to get input from @lognaturel on this as well.

[grzesiek2010]

Interesting let's see what @lognaturel thinks.

[lognaturel]

Here's an error message that I think would be helpful to someone in this state: "Downgrading ODK Collect is not supported. If you need the forms and data that ODK Collect currently manages, you must upgrade to the version you used previously or a newer version. If you don't need the data, you can uninstall this version and then reinstall it again."

Does that sound right? If so, let's go with something like that. It doesn't need to be translated.

[seadowg]

As discussed on a call, we're going to just throw an exception with a message like "App downgrade not supported" if onDowngrade is called.

[grzesiek2010]

As discussed on a call, we're going to just throw an exception with a message like "App downgrade not supported" if onDowngrade is called.

This exception is thrown by default by SQLiteOpenHelper if onDowngrade is not implemented:

throw new SQLiteException("Can't downgrade database from version " +
                oldVersion + " to " + newVersion);

I think it's enough we don't need to change it.