gh-108494: Build _testclinic_limited on Windows (#108589)

Add _testclinic_limited project to the Visual Studio solution:

* In "PCbuild/", copy "_asyncio.vcxproj" to "_testclinic_limited.vcxproj",
  replace "RootNamespace" with "_testclinic_limited", replace "_asyncio.c"
  with "_testclinic_limited.c".
* Open Visual Studio, open "PCbuild\pcbuild.sln", add the existing
  "PCbuild\_testclinic_limited.vcxproj" project to the solution.
* Add a dependency from "python" project to the "_testclinic_limited"
  project.
* Save and exit Visual Studio.
* Add ";_testclinic_limited" to "<TestModules Include="...">"
  in "PCbuild\pcbuild.proj".