MSVC Builds: Add NMake Makefiles to Build the Tests

This adds NMake Makefiles for one to build the tests for Visual Studio
builds, which is not done with an MSYS shell.  Shared items from the
existing NMake Makefiles for building the introspection files, which are
also used to build the tests, are split out into common NMake Makefiles,
which are then included.

This also means that we do not need to include the test_gir_cmd.txt for
people to look at when building the tests as the NMake Makefiles will do
the job for them, which cover the material there.
Visual Studio Projects: Don't Build the Test DLLs

The NMake Makefiles that build the tests cover these, so remove the parts
building the Test DLLs from the solution files.  This is done as a separate
commit as solution files must have DOS/Windows line endings, not UNIX line
endings.
MSVC Builds: Drop Test DLL Projects

This drops Visual Studio projects that does the build of the Test DLLs, as
the new NMake Makefiles will cover the building of them.  Please note that
the cmph test program is still built with the Visual Studio projects
though.