Microsoft.Testing.Extensions.CodeCoverage does not support MSBuild isolation

When building a MTP project with /isolate we are observing this issue:

C:\Users\X\.nuget\packages\microsoft.testing.extensions.codecoverage\18.1.0\buildMultiTargeting\Microsoft.Testing.Extensions.CodeCoverage.targets(18,5): error 
      MSB4252: Project "C:\src\Foo.csproj" with global properties
          (NuGetInteractive=true; IsGraphBuild=true)
          is building project "C:\src\Bar.csproj" with global properties
          (NuGetInteractive=true; IsGraphBuild=true)
          with the (InitializeSourceRootMappedPaths) target(s) but the build result for the built project is not in the engine cache. In isolated builds this could mean one of the following:
          - the reference was called with a target which is not specified in the ProjectReferenceTargets item in project "C:\src\Foo.csproj"
          - the reference was called with global properties that do not match the static graph inferred nodes
          - the reference was not explicitly specified as a ProjectReference item in project "C:\src\Foo.csproj"

https://github.com/dotnet/msbuild/blob/main/documentation/specs/static-graph.md#examples is missing instructions for SDK owners.

Start with the Microsoft.Testing.Extensions.CodeCoverage.targets path shown in the error and read the linked MSBuild static-graph specification, especially its examples. Reproduce an MTP build using /isolate and determine what support is missing for the InitializeSourceRootMappedPaths target. Done means the isolated build no longer reports MSB4252.