cmState: Move TargetType enum to separate namespace

Source/cmAddExecutableCommand.cxx

Source/cmAddLibraryCommand.cxx

Source/cmCPluginAPI.cxx

Source/cmCommonTargetGenerator.cxx

Source/cmComputeLinkDepends.cxx

Source/cmComputeLinkInformation.cxx

Source/cmComputeTargetDepends.cxx

Source/cmCoreTryCompile.cxx

Source/cmCoreTryCompile.h

Source/cmCustomCommandGenerator.cxx

Source/cmExportBuildAndroidMKGenerator.cxx

Source/cmExportBuildFileGenerator.cxx

Source/cmExportCommand.cxx

Source/cmExportFileGenerator.cxx

Source/cmExportInstallAndroidMKGenerator.cxx

Source/cmExportInstallFileGenerator.cxx

Source/cmExportLibraryDependenciesCommand.cxx

Source/cmExportTryCompileFileGenerator.cxx

Source/cmExtraCodeBlocksGenerator.cxx

Source/cmExtraCodeLiteGenerator.cxx