Implement auto-completion with valid entries from solver errors

Valid entries returned in Fatal Error as completion candidates

• Press "space/tab" after a keyword
• The language server inserts a dummy value; runs the solver and collects "Valid entries/models"
• Return valid entries as completion candidates

Additional context

• As diagnostics coming from OpenFOAM errors are not document-wise, the code has to check the document URI and cursor position before providing any candidates
• What to add as dummy value is tricky. Particularly, deciding when to add ";" will be problematic.
• Including valid entries shipped in custom shared libraries ($FOAM_USER_LIBBIN) can also be considered
  • With (possibly) automatic adding of the correct library to controlDict