Improve circular import error message

[marcauberer]

Improve circular import error message
Those error messages look like this:

[Error|Semantic] ../source2.spice:1:1:
Circular import detected: Circular import detected while importing 'source.spice':

*-----*
|     |
|  source2.spice
|     |
|  source1.spice
|     |
|  source.spice
|     |
*-----*

1  import "source" as s;
   ^^^^^^^^^^^^^^^^^^^^^