Store multiple queries on variant analysis object

[robertbrignull]

The idea here is to update the VariantAnalysis to store info for multiple queries. When showing the results view or otherwise displaying anything about the variant analysis, we just use data for the first query. The intention of this PR is that everything should work exactly as before when there's only one query, but it's not expected to do anything sensible yet when there are multiple queries.

Also note that this is just changing the internal type, and this PR isn't changing the query history types or any other data that is stored or sent outside of the extension.

This PR did end up a little larger than I expected it to. I wasn't expecting this change to the type to affect so many places. Wherever I've had to put in a hack of using the first query, I've added a TODO comment. My hope is that we can go through and remove these as we convert the rest of the extension to handle multiple queries.

Checklist

• CHANGELOG.md has been updated to incorporate all user visible changes made by this pull request.
• Issues have been created for any UI or other user-facing changes made by this pull request.
• [Maintainers only] If this pull request makes user-facing changes that require documentation changes, open a corresponding docs pull request in the github/codeql repo and add the ready-for-doc-review label there.

[robertbrignull]

I've pulled out part of this to #3287

[robertbrignull]

I'll close this PR since it's become a bit stale, and if we want to reproduce it then making the changes again isn't hard.