Emit submission payload(s) to host app

[eyelidlessness]

Supersedes and closes #289. Closes #23. Closes #290.

I have verified this PR works in these browsers (latest versions):

• Chrome
• Firefox
• Safari (macOS)
• Safari (iOS)
• Not applicable

It would shock me if there's anything browser-specific here.

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

Types do much of the work. Added console logs in FormPreview.vue demonstrate both handlers working.

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

I mentioned this in Slack, and will reiterate here: in hindsight, since there are two distinct SubmissionResult payload formats, events may not be the best API for this. On the other hand, it may be possible to improve the API by:

• Making submissionMaxSize generic at the component/package boundary
• Restoring the single submit event emit, implicitly branching the payload type so it's chunked if submissionMaxSize is non-nullish, monolithic otherwise

This change already felt big enough (especially compared to the #289 1-liner), so I didn't want to hold it up to explore that. Especially because I'm already kind of uncomfortable with the implicit coupling between a prop and emit, and I'm not sure branching on the prop would ameliorate that!

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 think of anything beyond... this exposes existing functionality to a host application, along with any known or unknown bugs that may already be present.

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

N/A

What's changed

The main @getodk/web-forms component now:

• Emits a MonolithicSubmissionResult if a host application attaches a submit event handler
• Adds an optional submissionMaxSize prop
• Emits a ChunkedSubmissionResult if a host application specifies submissionMaxSize and attaches a submitChunked event handler

[changeset-bot]

🦋 Changeset detected

Latest commit: c60e37a

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 2 packages

Name	Type
@getodk/web-forms	Minor
@getodk/xforms-engine	Patch

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[latin-panda]

It looks good to me! Just one question below but other than that, it's approved.