VS: Always initialize CMAKE_CONFIGURATION_TYPES in IDE generators

Initialize the CMAKE_CONFIGURATION_TYPES cache entry early during
EnableLanguage like the Xcode generator does.  Avoid depending on
the MSVC compiler information module to do it.  Otherwise code like

  project(MyProj NONE)

sets CMAKE_CONFIGURATION_TYPES late (in GenerateConfigurations), and
to only "Debug" and "Release" instead of the standard set of 4.

Reported-by: Paul Smith <paul@mad-scientist.net>
Merge topic 'vs-configurations' into next

42bb42d VS: Always initialize CMAKE_CONFIGURATION_TYPES in IDE generators