Test all combinations of source/target for scoping

[lars-reimann]

Is your feature request related to a problem? Please describe.
Currently, only a subset of possible combinations of source/target for cross-references is checked.

Also, test the import system separately and only once.

Tasks

• Test global scoping separately
• Think whether we can define tests for local scoping by a convention like we do for issue finder/formatter (linking done by ID):

// target 1
val »ref« = 1;

// source 1
»ref«;

[lars-reimann]

Superseded by #540.