Implement `when` clause for debugger contribution points to turn them off on virtual workspaces

[brettcannon]

microsoft/vscode#133146 and microsoft/vscode#133574

[karrtikr]

@isidorn I have been trying to add this in the Python extension but the when clause does not seem to be shutting off the debugger contributions for me.

I expected the following to have the same behavior as if I removed the contribution when not using a Web browser:

But Python option is still presented when attempting to debug as opposed to if the contribution is removed,

Thoughts?

[isidorn]

@karrtikr good catch, this is a minor bug for only that UI piece which I think we can fix easily. I have created this issue microsoft/vscode#133957
The rest of the UI should be disabled. Are you seeing any other UI contribution which should not be there?

Here are some ideas for context keys which you could potentially use here:

• Use the virtualWorkspace context variable to find out if the current workspace is a non-file system workspace.
• Use resourceScheme to check if the current resource is a file resource.
• Use shellExecutionSupported if there is a platform shell present.
• Advanced: Extensions can also define their own context keys

Thanks a lot for working on this 👏