refactor(vscode): migrate tests to typescript

[ocavue]

Changes

Migrate the @vscode/test-cli test (based on mocha) from .js to .mts in packages/language-tools/vscode/

This is the same change as my previous PR #16417

Part of #16241

Testing

• Ran test locally on my Mac
• CI is passed, as shown below

Docs

N/A

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