PackageDependencySerializerPlugin to detect files coming from packages and add dependency

If a step refers to a file (using e.g. FilePathAttribute). The serializer should try to match that to files from installed packages. If the files is from a package, that package should be added to the <Pachage.Dependencies> section in the bottom of the test plan xml file.

<TestPlan>
   <Steps>
      <ReferenceTestPlanStep>
         <TestPlan>Packages/A/MySubTestPlan.TapPlan</TestPlan>
      </ReferenceTestPlanStep>
   </Steps>
   <PackageDependencies> 
      <PackageDependency PackageName="A">
          <Type Name="A.X"/>
          <File Name="Packages/A/hej.wfm"/>
          <File Name="Packages/A/MySubTestPlan.TapPlan"/>
      </PackageDependency>
   </PackageDependencies>
</TestPlan>