Give better feedback when META-INF/RASCAL.MF is missing

[PaulKlint]

When a Rascal project is missing META-INF/Rascal.MF the following messages is given (which is very good):

Unfortunately this gives no actionable perspective to the user.

Possible improvements:

• Add in the message text a link to the documentation where this is described.
• Add in the message text the suggested contents of RASCAL.MF.
• Add the option to fix this automatically

[jurgenvinju]

Note that on the no-lib branch this message is produced by the PathConfig class. We could attach a fix command easily there and add its execution to the rascal-lsp Actions module.

Or both: this is on a module location, the typesvript code can add the quickfix command "generateRascalMf(LOC)"