Add "View Autofixes" feature for variant analysis results

[jcogs33]

Description

Adds a "View Autofixes" feature for variant analysis results. This is a canary-only feature.
Generates autofixes for selected variant analysis results and opens the resulting autofix outputs in a markdown file.
Activated via the "View Autofixes" button in the variant analysis webview or via right-clicking the variant analysis query history item.

At a high-level, the implementation:

• Checks for a local checkout of autofix
• Sets up to run autofix by:
  • Overriding the relevant query help
  • Getting the relevant SARIF(s)
  • Downloading source root(s)
• Runs autofix locally
• Outputs autofix results in a markdown file

Commit-by-commit review recommended. Let me know if you want me to split anything onto a separate PR.

Consideration

• See in-line comments
• Change from my original implementation: Instead of downloading databases and then extracting the source root from the database, I directly download the source root since it seemed a bit faster. Let me know if you think the database approach is better.
• I will make a follow-up PR to convert this to support Go autofix instead of cocofix, and I'll update the queryHelpOverrideDirectory to the new go/pkg/autofix/prompt/qhelps directory in that PR.

Testing

• I've manually tested this feature but have not added unit/view/integration tests since it seems another canary feature did not add tests. Let me know if I should add tests after all.
• Note: There is a known issue with the E2E CI test failing. It is not caused by changes in this PR.

[jcogs33]

There's one more comment from @koesie10 that should be addressed

@aeisenberg Which comment are you referring to? There were four things I still was planning to address: three comments related to editing parts of downloadPublicCommitSource, and one comment about getting the autofix CLI logs into the extension logs.

[aeisenberg]

Oh...there might be more things that I missed. I'm out tomorrow. I think it's also a holiday in the US, so I can take another look on Monday.

[jcogs33]

@aeisenberg @koesie10 I've addressed all review comments. Let me know if you want any other changes, especially regarding the environment variables.

[koesie10]

Thanks, this looks good to me. I have some optional comments, but I don't think any of those are necessary.

[aeisenberg]

Looks generally good. I see one area where I think you can simplify things.

[jcogs33]

@koesie10 @aeisenberg I've responded to all new review comments. Thanks for the thorough reviews! 🙇

[koesie10]

LGTM, thanks!

[aeisenberg]

Great job!

I haven't tried this locally, but the code looks good. It's likely that the failing E2E job is transient. I'll kick it off again and hopefully it will work.

[jcogs33]

@aeisenberg There's a known issue with the E2E tests failing since end of March. The issue tracking it is in the private code-scanning repo. So I think this PR can be merged despite that test failure?

[aeisenberg]

I'm fine with that.