Reenable TestDbgEng tests in M.D.DebugServices.UnitTests

[mikem8361]

After upgrading to clrmd 2.1 in PR #3094 the DebugServices unit tests could no longer load dbgeng.dll:

xUnit.net Console Runner v2.4.2-pre.9+e627c231a5 (64-bit .NET 6.0.5)
  Discovering: Microsoft.Diagnostics.DebugServices.UnitTests
  Discovered:  Microsoft.Diagnostics.DebugServices.UnitTests
  Starting:    Microsoft.Diagnostics.DebugServices.UnitTests
    Microsoft.Diagnostics.DebugServices.UnitTests.DebugServicesTests.RuntimeTests(host: DbgEng: D:\a\_work\1\s\.packages\testassets.windows.x64.5.0\1.0.257801\content\DualRuntimes\SOS.DualRuntimes.Heap.dmp) [FAIL]
      System.DllNotFoundException : LoadLibrary(D:\a\_work\1\s\.packages\cdb-sos\10.0.18362\runtimes\win-x64\native\dbgeng.dll) failed 127
      Stack Trace:
        /_/src/tests/Microsoft.Diagnostics.DebugServices.UnitTests/TestDbgEng.cs(64,0): at Microsoft.Diagnostics.DebugServices.UnitTests.TestDbgEng.DbgEngController..ctor(String dbgengPath, String dumpPath, String sosPath)
        /_/src/tests/Microsoft.Diagnostics.DebugServices.UnitTests/TestDbgEng.cs(26,0): at Microsoft.Diagnostics.DebugServices.UnitTests.TestDbgEng.GetTarget()
        /_/src/Microsoft.Diagnostics.TestHelpers/TestHost/TestHost.cs(30,0): at Microsoft.Diagnostics.TestHelpers.TestHost.get_Target()
        /_/src/tests/Microsoft.Diagnostics.DebugServices.UnitTests/DebugServicesTests.cs(260,0): at Microsoft.Diagnostics.DebugServices.UnitTests.DebugServicesTests.RuntimeTests(TestHost host)
      Output:
        xunit.console Information: 0 : DbgEngController: D:\a\_work\1\s\.packages\cdb-sos\10.0.18362\runtimes\win-x64\native\dbgeng.dll D:\a\_work\1\s\.packages\testassets.windows.x64.5.0\1.0.257801\content\DualRuntimes\SOS.DualRuntimes.Heap.dmp D:\a\_work\1\s\artifacts\bin\Windows_NT.x64.Debug\sos.dll
    Microsoft.Diagnostics.DebugServices.UnitTests.DebugServicesTests.TargetTests(host: DbgEng: D:\a\_work\1\s\.packages\testassets.windows.x64.5.0\1.0.257801\content\DualRuntimes\SOS.DualRuntimes.Heap.dmp) [FAIL]
      System.DllNotFoundException : LoadLibrary(D:\a\_work\1\s\.packages\cdb-sos\10.0.18362\runtimes\win-x64\native\dbgeng.dll) failed 127
      Stack Trace:
        /_/src/tests/Microsoft.Diagnostics.DebugServices.UnitTests/TestDbgEng.cs(64,0): at Microsoft.Diagnostics.DebugServices.UnitTests.TestDbgEng.DbgEngController..ctor(String dbgengPath, String dumpPath, String sosPath)
        /_/src/tests/Microsoft.Diagnostics.DebugServices.UnitTests/TestDbgEng.cs(26,0): at Microsoft.Diagnostics.DebugServices.UnitTests.TestDbgEng.GetTarget()
        /_/src/Microsoft.Diagnostics.TestHelpers/TestHost/TestHost.cs(30,0): at Microsoft.Diagnostics.TestHelpers.TestHost.get_Target()
        /_/src/tests/Microsoft.Diagnostics.DebugServices.UnitTests/DebugServicesTests.cs(58,0): at Microsoft.Diagnostics.DebugServices.UnitTests.DebugServicesTests.TargetTests(TestHost host)
      Output:
        xunit.console Information: 0 : DbgEngController: D:\a\_work\1\s\.packages\cdb-sos\10.0.18362\runtimes\win-x64\native\dbgeng.dll D:\a\_work\1\s\.packages\testassets.windows.x64.5.0\1.0.257801\content\DualRuntimes\SOS.DualRuntimes.Heap.dmp D:\a\_work\1\s\artifacts\bin\Windows_NT.x64.Debug\sos.dll
    Microsoft.Diagnostics.DebugServices.UnitTests.DebugServicesTests.ModuleTests(host: DbgEng: D:\a\_work\1\s\.packages\testassets.windows.x64.5.0\1.0.257801\content\DualRuntimes\SOS.DualRuntimes.Heap.dmp) [FAIL]
      System.DllNotFoundException : LoadLibrary(D:\a\_work\1\s\.packages\cdb-sos\10.0.18362\runtimes\win-x64\native\dbgeng.dll) failed 127
      Stack Trace:
        /_/src/tests/Microsoft.Diagnostics.DebugServices.UnitTests/TestDbgEng.cs(64,0): at Microsoft.Diagnostics.DebugServices.UnitTests.TestDbgEng.DbgEngController..ctor(String dbgengPath, String dumpPath, String sosPath)
        /_/src/tests/Microsoft.Diagnostics.DebugServices.UnitTests/TestDbgEng.cs(26,0): at Microsoft.Diagnostics.DebugServices.UnitTests.TestDbgEng.GetTarget()
        /_/src/Microsoft.Diagnostics.TestHelpers/TestHost/TestHost.cs(30,0): at Microsoft.Diagnostics.TestHelpers.TestHost.get_Target()
        /_/src/tests/Microsoft.Diagnostics.DebugServices.UnitTests/DebugServicesTests.cs(75,0): at Microsoft.Diagnostics.DebugServices.UnitTests.DebugServicesTests.ModuleTests(TestHost host)
      Output:
        xunit.console Information: 0 : DbgEngController: D:\a\_work\1\s\.packages\cdb-sos\10.0.18362\runtimes\win-x64\native\dbgeng.dll D:\a\_work\1\s\.packages\testassets.windows.x64.5.0\1.0.257801\content\DualRuntimes\SOS.DualRuntimes.Heap.dmp D:\a\_work\1\s\artifacts\bin\Windows_NT.x64.Debug\sos.dll
    Microsoft.Diagnostics.DebugServices.UnitTests.DebugServicesTests.ThreadTests(host: DbgEng: D:\a\_work\1\s\.packages\testassets.windows.x64.5.0\1.0.257801\content\DualRuntimes\SOS.DualRuntimes.Heap.dmp) [FAIL]
      System.DllNotFoundException : LoadLibrary(D:\a\_work\1\s\.packages\cdb-sos\10.0.18362\runtimes\win-x64\native\dbgeng.dll) failed 127
      Stack Trace:
        /_/src/tests/Microsoft.Diagnostics.DebugServices.UnitTests/TestDbgEng.cs(64,0): at Microsoft.Diagnostics.DebugServices.UnitTests.TestDbgEng.DbgEngController..ctor(String dbgengPath, String dumpPath, String sosPath)
        /_/src/tests/Microsoft.Diagnostics.DebugServices.UnitTests/TestDbgEng.cs(26,0): at Microsoft.Diagnostics.DebugServices.UnitTests.TestDbgEng.GetTarget()
        /_/src/Microsoft.Diagnostics.TestHelpers/TestHost/TestHost.cs(30,0): at Microsoft.Diagnostics.TestHelpers.TestHost.get_Target()
        /_/src/tests/Microsoft.Diagnostics.DebugServices.UnitTests/DebugServicesTests.cs(212,0): at Microsoft.Diagnostics.DebugServices.UnitTests.DebugServicesTests.ThreadTests(TestHost host)
      Output:
        xunit.console Information: 0 : DbgEngController: D:\a\_work\1\s\.packages\cdb-sos\10.0.18362\runtimes\win-x64\native\dbgeng.dll D:\a\_work\1\s\.packages\testassets.windows.x64.5.0\1.0.257801\content\DualRuntimes\SOS.DualRuntimes.Heap.dmp D:\a\_work\1\s\artifacts\bin\Windows_NT.x64.Debug\sos.dll
  Finished:    Microsoft.Diagnostics.DebugServices.UnitTests
=== TEST EXECUTION SUMMARY ===
   Microsoft.Diagnostics.DebugServices.UnitTests  Total: 83, Errors: 0, Failed: 4, Skipped: 0, Time: 171.750s
=== COMMAND LINE ===
"D:\a\_work\1\s\.dotnet\dotnet.exe" exec --depsfile "D:\a\_work\1\s\artifacts\bin\Microsoft.Diagnostics.DebugServices.UnitTests\Debug\net60\Microsoft.Diagnostics.DebugServices.UnitTests.deps.json" --runtimeconfig "D:\a\_work\1\s\artifacts\bin\Microsoft.Diagnostics.DebugServices.UnitTests\Debug\net60\Microsoft.Diagnostics.DebugServices.UnitTests.runtimeconfig.json"  "D:\a\_work\1\s\.packages\xunit.runner.console/2.4.2-pre.9/tools/netcoreapp2.0/xunit.console.dll" "D:\a\_work\1\s\artifacts\bin\Microsoft.Diagnostics.DebugServices.UnitTests\Debug\net60\Microsoft.Diagnostics.DebugServices.UnitTests.dll" -noautoreporters -xml "D:\a\_work\1\s\artifacts\TestResults\Debug\Microsoft.Diagnostics.DebugServices.UnitTests_net60_x64.xml" -html "D:\a\_work\1\s\artifacts\TestResults\Debug\Microsoft.Diagnostics.DebugServices.UnitTests_net60_x64.html"  > "D:\a\_work\1\s\artifacts\log\Debug\Microsoft.Diagnostics.DebugServices.UnitTests_net60_x64.log" 2>&1