fix yop project for latest VScode release

[jurgenvinju]

Describe the bug

This does not break the code, but since we have ultimate beginners looking at these files, it could be confusing to read the new (otherwise very helpful) message.

[DavyLandman]

I don't think this is a VS Code bug right? Looks more like a specific example project that needs to be updated?

[jurgenvinju]

I posted it here to signal that we may have some (important) downstream projects that are now broken with the latest VScode extension without us realizing it. This one has hundreds of users, for example.

Is a missing pom.xml file really breaking the extension? I think we might need a softer message for a missing pom file, as compared to a missing RASCAL.MF file.

[DavyLandman]

It's already a warning, but yes, if you are missing a pom.xml, some of your dependencies might not be picked up. (like say you did edit your rascal.mf to have a dependency).

Can we make better diagnostics? Yes. I would also ideally like us to have a quickfix for the problems we know how to fix..

[DavyLandman]

@jurgenvinju I think the latest fixes to the validators fixed this, can you make sure?