C# auto-generated header for generated c# codec files (#814)

* Added "auto-generated" tag which is recognized by Visual Studio at the top of each generated C# file.
Auto-generated files are not included in automatic code-cleanup and/or inspection processes.

* Renamed all generated *.cs files to *.g.cs
Like the auto-generated tag in the file's header, this causes files to be recognized as auto-generated code by Visual Studio.
An added bonus of the filename change is that these files can be treated differently based on the filename in your project's .gitignore or .editorconfig files

Author: mhoogveld

sbe-tool/src/main/java/uk/co/real_logic/sbe/generation/csharp/CSharpGenerator.java

@@ -614,7 +614,9 @@ private CharSequence generateFileHeader(final String packageName)
         }
 
         return String.format(
-            "/* Generated SBE (Simple Binary Encoding) message codec */\n\n" +
+            "// <auto-generated>\n" +
+            "//     Generated SBE (Simple Binary Encoding) message codec\n" +
+            "// </auto-generated>\n\n" +
             "#pragma warning disable 1591 // disable warning on missing comments\n" +
             "using System;\n" +
             "using Org.SbeTool.Sbe.Dll;\n\n" +

sbe-tool/src/main/java/uk/co/real_logic/sbe/generation/csharp/CSharpNamespaceOutputManager.java

@@ -71,7 +71,7 @@ public CSharpNamespaceOutputManager(final String baseDirName, final String packa
      */
     public Writer createOutput(final String name) throws IOException
     {
-        final File targetFile = new File(outputDir, name + ".cs");
+        final File targetFile = new File(outputDir, name + ".g.cs");
         return Files.newBufferedWriter(targetFile.toPath(), StandardCharsets.UTF_8);
     }
 }