VS: Add support for NATVIS files

Add an explicit `<Natvis>` element in VS project files for `*.natvis`
files.  These enable custom debug visualizers for project-specific
types.

Fixes #16043.

Help/release/dev/vs-natvis.rst

@@ -0,0 +1,5 @@
+vs-natvis
+---------
+
+* :ref:`Visual Studio Generators` for VS 2010 and above learned to
+  place ``.natvis`` source files into VS project files properly.

Source/cmVisualStudio10TargetGenerator.cxx

@@ -1187,6 +1187,8 @@ void cmVisualStudio10TargetGenerator::WriteExtraSource(cmSourceFile const* sf)
     tool = "PRIResource";
   } else if (ext == "xml") {
     tool = "XML";
+  } else if (ext == "natvis") {
+    tool = "Natvis";
   }
 
   if (this->NsightTegra) {