Need to return SourceRoot Items to for referenced projects

[clairernovotny]

Version Used:
Latest

We need to return the SourceRoot items calculated by InitializeSourceRootMappedPaths so that other tools can access the map outside of the immediate project. No target returns the SourceRoot items today.

This was needed to enable Coverlet, and likely other tools to work. Coverlet had to get the SourceRoot items for each of the projects referenced by a test project.

@tmat and I worked with @MarcoRossignoli to come up with a solution. To work, we need to either add a new target like this:

  <Target Name="GetPathMap"
          DependsOnTargets="InitializeSourceRootMappedPaths"
          Returns="@(_LocalTopLevelSourceRoot)"
          Condition="'$(DeterministicSourcePaths)' == 'true'">
    <ItemGroup>
      <_LocalTopLevelSourceRoot Include="@(SourceRoot)" Condition="'%(SourceRoot.NestedRoot)' == ''"/>
    </ItemGroup>
  </Target>  

Or return the SourceRoot's from InitializeSourceRootMappedPaths directly.

See coverlet-coverage/coverlet#363

[clairernovotny]

Can we get this into 3.1.xxx servicing?

[clairernovotny]

Ping on servicing? This affects code coverage tools that will need this data.

[tmat]

@dsplaisted @jaredpar

[clairernovotny]

Jared answered in the PR, master goes to both 5.0.xxx and 3.1.xxx branches, so the answer is yes.