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

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);
     }
 }