Introduce a DTO for exporting dependency information.

The structure of the raw dependency information spit out by ksb::DependencyResolver is not suitable to expose to clients directly.
It simply is too tightly coupled to Perl code and kdesrc-build in particular.

By introducing a DTO to define the wire format for exported information, we get much cleaner output that is unambiguous and can be exported safely to clients.
2 jobs for dependency-graph-dto in 2 minutes and 52 seconds (queued for 3 seconds)
Status Job ID Name Coverage
  Test
passed #16429
smoke-test

00:02:52

passed #16428
unit-test

00:01:57