VS: improve handling of source files with special extensions in .csproj

Mainly <Link> and <DependentUpon> tags are added to connect generated
and manually edited files. Special file extensions that are take care
of are:

 - .Designer.cs
 - .xaml.cs
 - .settings
 - .resx
 - .xaml

Help/release/dev/vs-advanced-source-properties.rst

@@ -0,0 +1,12 @@
+vs-advanced-source-properties
+-----------------------------
+
+* The :ref:`Visual Studio Generators` for VS 2010 and above
+  learned some more source file properties:
+
+  - :prop_sf:`VS_RESOURCE_GENERATOR` (C# only): allows setting the resource
+    generator
+  - :prop_sf:`VS_COPY_TO_OUT_DIR`: parameter to set if file should be copied
+    to output directory (values: ``Never``, ``Always``, ``PreserveNewest``)
+  - :prop_sf:`VS_INCLUDE_IN_VSIX`: boolean property to include file include
+    Visual Studio extension package

Help/release/dev/vs-csharp-support.rst

@@ -19,7 +19,16 @@ vs-native-csharp-support
   that specifically targets C# contains ``CSharp`` as a part of
   their names.
 
-* More finetuning of C# targets can be done using target
-  properties. Specifically the Visual Studio related target
+* More finetuning of C# targets can be done using target and source
+  file properties. Specifically the Visual Studio related target
   properties (``VS_*``) are worth a look (for setting toolset
   versions, root namespaces, assembly icons, ...).
+
+* **Auto-"linking"** in .csproj files: In C#/.NET development with
+  Visual Studio there is a number of visual editors used which
+  generate code. Both the generated files and the ones edited
+  with the UI are connected in the ``.csproj`` file using
+  ``<DependentUpon>`` tags. If CMake finds within a C# project
+  any source file with extension ``.Designer.cs`` or ``.xaml.cs``,
+  it checks sibling files with extension ``.xaml``, ``.settings``,
+  ``.resx`` or ``.cs`` and establishes the dependency connection.