Allow in-progress form upload to be interrupted on cancel

[grzesiek2010]

Closes #7188

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

In #7008 we reworked the process of uploading filled forms manually by replacing the old Android AsyncTask with coroutines. The old approach was checking if the task is active at the beginning of every iteration (for every selected form) and we implemented the same behavior in the coroutine-based approach. However, it turns out that the old AsyncTask, when canceled, was also interrupting the worker thread, which had the effect of canceling a form upload that was already in progress (mid-upload). We missed that in the new approach, and now I have fixed it by using runInterruptible.

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?

We need to test the same things as in #7008.

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

Any form.

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]

#7203 (comment)

[seadowg]

I'm wondering if we can introduce a generalization for this instead that builds on Cancellable - could be a CancellationToken class like this:

class CancellationToken : Cancellable {

    private var cancelled = false

    override fun cancel() {
        cancelled = true
    }

    fun ensureActive() {
        if (isCancelled()) {
            throw CancelledException()
        }
    }
}

Or just something similar!

[grzesiek2010]

I gave this a go, but I'd lean towards keeping the current approach. A CancellationToken would complicate the code, and it would decouple cancellation from the coroutine, so we'd drop the built-in mechanism (isCancelled = { !isActive }) we get for free.