Add target label to layering check violation message

[adincebic]

Previously the layering check violation would only report the Swift module name that is not directly declared as a dependency.
Now we make sure that target label is captured and displayed to the user so that it is easier to act upon it.

Previously:

error: Layering violation in @@//test/fixtures/layering_check:layering_violation
The following modules were imported, but they are not direct dependencies of the target:

    TransitiveDependency

Please add the correct 'deps' to @@//test/fixtures/layering_check:layering_violation to import those modules.

now:

error: Layering violation in @@//test/fixtures/layering_check:layering_violation
The following modules were imported, but they are not direct dependencies of the target:

    TransitiveDependency (@@//test/fixtures/layering_check:TransitiveDependency)

Please add the correct 'deps' to @@//test/fixtures/layering_check:layering_violation to import those modules.

Users can now add the dependency way quicker and there could even be an automated way to add the missing dep since the label is present.