Include primary instance root attributes, namespace declarations in submission XML

[eyelidlessness]

Closes #286.

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

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

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

• Added tests for attributes
• Updated tests for XML namespace declarations

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

It'd be better to have a more general solution for both attributes and namespace declarations.

Both would involve significant work on both parsing (to capture attributes and namespace prefixes/declarations throughout the primary instance subtree), as well as the primary instance state data model (as we don't have a concept of attributes, and presently ignore non-default-namespace element names).

I'd be remiss if I failed to mention that there would have been an even hacker way to deal with namespace declarations: abuse built-in DOM serialization (as it functionally does the same thing to derive namespaces as this change does more explicitly). I didn't do this because:

• It'd be a lot less clear what's happening and why
• I don't think it's standardized in any way, and I wouldn't be surprised if jsdom/any other DOM-compat library would make that technique unreliable

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?

It's possible that even the simplified solution has ignored some edge case, which would be most likely around namespaces. I think I was fairly thorough, but the parse-stage collection of namespaces in a temporary map would be the most likely suspect.

It's also possible some logical error might have introduced subtle fallibility. I'm hopeful that letting the type system guide the change avoided most if not all of that risk.

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

I think any form will do?

What's changed

• Static attributes on the primary instance root element are parsed, and re-serialized on submission
• Namespace declarations are parsed (or derived) on the primary instance root element, also re-serialized on submission

[changeset-bot]

🦋 Changeset detected

Latest commit: b576ec4

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

This PR includes changesets to release 3 packages

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

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[lognaturel]

I should have checked what Collect and Enketo do with namespaces in submissions before commenting! Neither includes the default namespace declaration. I don't think it will break any existing systems to include but it does add more noise.

I'm inclined to go with this for now and come back to it if we see any issues. Alternately, we could special case the default namespace, maybe?