Detect and warn about an incorrect project setup

This module now checks for some common errors:

rascal file opened that is not part of any of the projects active in the workspace
rascal file without a pom.xml in the right position
rascal file without a rascal.mf in the right place
rascal file in a path not defined in the rascal.mf sources key.

Some screenshots:

Btw, yes, we could do this in rascal with some validation, but that would involve another extension on the LSP protocol. Until we've grown the checker to deal with this properly, we can help the user make less mistakes.

Ideally we would also add some quick fixes, but that's not always so simple to figure out.

This prevents cases like #410 and #341, or at least leaves the user less confused.

usethesource / rascal-language-servers

Detect and warn about an incorrect project setup #411

Quality Gate passed