(GH-793) Add simple folding range provider capability

This commit adds the skeleton for a Folding Range Provider.

Author: glennsarti

src/PowerShellEditorServices.Protocol/LanguageServer/ServerCapabilities.cs

@@ -42,6 +42,8 @@ public class ServerCapabilities
         public ExecuteCommandOptions ExecuteCommandProvider { get; set; }
 
         public object Experimental { get; set; }
+
+        public bool? FoldingRangeProvider { get; set; }
     }
 
     /// <summary>

src/PowerShellEditorServices.Protocol/Server/LanguageServer.cs

@@ -239,7 +239,8 @@ await requestContext.SendResult(
                         },
                         DocumentFormattingProvider = false,
                         DocumentRangeFormattingProvider = false,
-                        RenameProvider = false
+                        RenameProvider = false,
+                        FoldingRangeProvider = true
                     }
                 });
         }