When no workspace and metals cannot start show error message in a more visible place about metals-vscode

[Sporarum]

Going to Output -> Metals does reveal the cause of the issue:
"Metals will not start because you've opened a single file and not a project directory."

This message should not be hidden there !

And furthermore, replacing the "no data provider" message by that message would not completely fix the situation, as the "New Scala Project" button, and the "Help and Feedback" section would still not be present.

Therefore I think instead Metals should run in a simplified mode when outside a folder, just enough to enable users to create a project.

[kasiaMarek]

This message should not be hidden there !

We can show the message in a more visible manner and provide information on should the user do as a temporary solution.

Therefore I think instead Metals should run in a simplified mode when outside a folder, just enough to enable users to create a project.

For those we already have issues:
#357
scalameta/metals-feature-requests#231
and there is some in progress work to allow metals to work without a workspace:
scalameta/metals#5531 (unfortunately currently blocked on a semanticdb issue)