Fix breakage v3.0 caused to the InterSystems Testing Manager extension

[gjsjohnmurray]

This PR fixes #1618

[isc-bsaviano]

@gjsjohnmurray Can you explain why this is necessary? Why can't the testing manager sync the files itself?

[gjsjohnmurray]

I'd prefer not to have to make the Testing Manager have to deal with /api/atelier file- and directory-type endpoints directly. But perhaps I can make it talk to isfs://server/_vscode/NAMESPACE/foo.bar?csp URLs directly instead of using isfs://server/.vscode/foo.bar and relying on the the redirection (which is what's no longer happening for client-type workspaces since #1479). I'll try this out in Testing Manager.

[isc-bsaviano]

Yeah, I can see why it would be easier to use vscode.workspace.fs on isfs URIs. I think using /_vscode directly should work though, assuming there really is a /_vscode web app on that server.

[gjsjohnmurray]

I worked around it in the other extension so I'm closing this unmerged.