CPack: Add NuGet support

Create a CPack generator that uses `nuget.exe` to create packages:

    https://docs.microsoft.com/en-us/nuget/what-is-nuget

NuGet packages could be easily produced from a `*.nuspec` file (running
`nuget pack` in the directory w/ the spec file).  The spec filename does
not affect the result `*.nupkg` name -- only `id` and `version` elements
of the spec are used (by NuGet).

Some implementation details:

* Minimize C++ code -- use CMake script do to the job. It just let the
  base class (`cmCPackGenerator`) to preinstall everything to a temp
  directory, render the spec file and run `nuget pack` in it, harvesting
  `*.nupkg` files...;

* Ignore package name (and use default paths) prepared by the base class
  (only `CPACK_TEMPORARY_DIRECTORY` is important) -- final package
  filename is a responsibility of NuGet, so after generation just scan the
  temp directory for the result `*.nupkg` file(s) and update
  `packageFileNames` data-member of the generator;

* The generator supports _all-in-one_ (default), _one-group-per-package_
  and _one-component-per-package_ modes.

1 files changed, 37 insertions, 0 deletions

diff --git a/Source/CPack/cmCPackNuGetGenerator.h b/Source/CPack/cmCPackNuGetGenerator.h
new file mode 100644
index 0000000..a59db2d
--- /dev/null
+++ b/Source/CPack/cmCPackNuGetGenerator.h
@@ -0,0 +1,37 @@
+/* Distributed under the OSI-approved BSD 3-Clause License.  See accompanying
+   file Copyright.txt or https://cmake.org/licensing for details.  */
+#ifndef cmCPackNuGetGenerator_h
+#define cmCPackNuGetGenerator_h
+
+#include "cmCPackGenerator.h"
+
+/** \class cmCPackNuGetGenerator
+ * \brief A generator for RPM packages
+ */
+class cmCPackNuGetGenerator : public cmCPackGenerator
+{
+public:
+  cmCPackTypeMacro(cmCPackNuGetGenerator, cmCPackGenerator);
+
+  // NOTE In fact, it is possible to have NuGet not only for Windows...
+  // https://docs.microsoft.com/en-us/nuget/install-nuget-client-tools
+  static bool CanGenerate() { return true; }
+
+protected:
+  bool SupportsComponentInstallation() const override;
+  int PackageFiles() override;
+
+  const char* GetOutputExtension() override { return ".nupkg"; }
+  bool SupportsAbsoluteDestination() const override { return false; }
+  /**
+   * The method used to prepare variables when component
+   * install is used.
+   */
+  void SetupGroupComponentVariables(bool ignoreGroup);
+  /**
+   * Populate \c packageFileNames vector of built packages.
+   */
+  void AddGeneratedPackageNames();
+};
+
+#endif