Add VS Code Shell extension option to MSI

[George Ng (GeorgeNgMsft)]

Summary

Updates the MSI installer to add an option to install the VS Code Shell extension. Also adds ownership keys to correlate with each installation (Chat vs Shell) so we can eventually separate uninstall for both.

• add an interactive MSI checkbox and VSCODESHELL property for installing the TypeAgent VS Code Shell extension
• reuse the VS Code extension installer with separate ownership metadata and no desktop shortcut
• package, publish, and pass the Shell VSIX through local and release MSI builds
• add installer wiring tests to the regular local test command

Validation

• node --test tools/scripts/test/*.spec.mjs
• pnpm run build vscode-shell
• npm run package in packages/vscode-shell
• pnpm run code-complexity:ci
• pnpm run code-lint -- --ratchet --base origin/main
• PowerShell parser validation for install-vscode-chat.ps1
• Prettier checks for changed supported files