Use package.json to detect if workspace is vscode workspace

[hediet]

(see #285255)

FYI @connor4312

There is still this, which needs to be fixed:

vscode/.vscode/extensions/vscode-selfhost-test-provider/package.json

Lines 55 to 57 in 3dfd29a

	"activationEvents": [
	"workspaceContains:src/vs/loader.js"
	],

[Copilot]

Pull request overview

This PR updates the VS Code workspace detection logic to use package.json instead of checking for the existence of src/vs/loader.js. The new approach reads the package.json file and verifies the workspace by checking if the name field equals code-oss-dev, making the detection more reliable and explicit.

Key changes:

• Replaced file existence check (src/vs/loader.js) with package.json name validation
• Extracted detection logic into a new isVsCodeWorkspaceFolder function for better modularity
• Applied minor code formatting updates to empty braces

[connor4312]

This would actually be fine to activate onStartupFinished or * because it's now a workspace extension and we know it'll always be relevant