More explicitly print the context if a name cannot be resolved

[bobismijnnaam]

This PR improves the error message when a name cannot be resolved in some situations.

Example program:

class C {
    void m() {
        assert Perm(f, write);
    }
}

Old error:

At null: type error: defined type f not found
The final verdict is Error

New error:

At null: type error: defined type f not found
=== xx.pvl                         ===
   1 class C {
   2     void m() {
                        [-
   3         assert Perm(f, write);
                         -]
   4     }
   5 }
-----------------------------------------
  Unknown name
=========================================
The final verdict is Error

[sonarcloud]

Kudos, SonarCloud Quality Gate passed!   

0 Bugs
0 Vulnerabilities
0 Security Hotspots
0 Code Smells

25.0% Coverage
0.0% Duplication