VSCode: Fix local embeddings status for non-git workspaces, git repos w/out remotes

[dominiccooney]

• When opening a non-git repo, instead of the enhanced context selector showing a non-functional "enable embeddings" button, do not show local embeddings status.
• When opening a git repo without a remote, instead of showing a spinner indefinitely and "Indexed", show the circle-slash. Fixes bug: Local embeddings spins "indexed" forever in git repos without remotes #2217.
• During embeddings index generation, show the current file being indexed in the status bar item tooltip.
• If embeddings index generation fails, show the error message in a tooltip on the status bar. (Test coverage and improvements planned in a follow-up change.)

Adds e2e tests for the major cases above.

Also improves the e2e test framework:

• Fixes a race condition creating the workspace .vscode directory, and writing .vscode/settings.json. This sometimes meant the tests were running without the correct settings.
• Adds Playwright extensions so tests can configure an isolated working directory, extra VSCode settings, and treat the test server endpoint as "dotcom".
• Expands the mock server so that the consumer login path works.
• Adds testing hooks to local embeddings to use a mock server, embeddings model, and isolated index library path.
• Deletes obsolete helper for submitting sidebar chat messages.

Test plan

This integration test covers the scenarios of opening no git repo, a git repo without a remote, and a git repo with a remote and then generating embeddings for the repo and querying them:

pnpm test:e2e -- local-embeddings.test.ts

[toolmantim]

Verified that this all works as expected 👍🏼👏🏼 Two non-blocking notes…

When there's no origin:

it would be nicer to also show an explanation, similar to this state:

With the copy:

Git repository is missing a remote origin.

I would have assumed a similar UI if you open a folder that isn't a Git repo (with the copy "Folder is not a Git repository"), but instead I see the following:

[dominiccooney]

Thanks for the feedback! Love the wording of the error messages. I wrestled with it briefly but nothing sounded right.