Improve `debian/tests/control` support

[nthykier]

Steps:

• Auto-detect debian/tests/control as a relevant file
• Recognize fields (provide documentation and known keywords using existing features)
• Inspections:
  • Tests vs.Test-Command being mutually exclusive
  • needs-internet but missing flaky.
  • Tests-Directory should be a directory (or non-existent - the directory can be a build artifact)
  • Tests-Directory (effectively) set to debian/tests is redundant.
  • Restrictions: hint-testsuite-triggers should imply Test-Command: /bin/true (or there about. false have been seen in the wild as well) since the test will not be run anyway. With /usr-merge, /usr/bin/true (etc.) will probably appear too
  • Restrictions: needs-recommends should be Depends: @recommends@
• Auto-complete: Auto-complete Tests values relative to Test-Directory (defaulting to debian/tests)