Add -LanguageServiceOnly switch to disable debug service (#1640)

This is used by third party consumers.

Co-authored-by: Andy Schwartzmeyer <andrew@schwartzmeyer.com>

Author: dkattan

module/PowerShellEditorServices/Start-EditorServices.ps1

@@ -66,6 +66,9 @@ param(
     [switch]
     $DebugServiceOnly,
 
+    [switch]
+    $LanguageServiceOnly,
+
     [string[]]
     $AdditionalModules,
 

src/PowerShellEditorServices.Hosting/Commands/StartEditorServicesCommand.cs

@@ -182,6 +182,12 @@ public StartEditorServicesCommand()
         [Parameter]
         public SwitchParameter DebugServiceOnly { get; set; }
 
+        /// <summary>
+        /// When set, do not enable debug adapter, only the language service.
+        /// </summary>
+        [Parameter]
+        public SwitchParameter LanguageServiceOnly { get; set; }
+
         /// <summary>
         /// When set with a debug build, startup will wait for a debugger to attach.
         /// </summary>
@@ -465,6 +471,12 @@ private ITransportConfig GetDebugServiceTransport()
         {
             _logger.Log(PsesLogLevel.Diagnostic, "Configuring debug transport");
 
+            if (LanguageServiceOnly)
+            {
+                _logger.Log(PsesLogLevel.Diagnostic, "No Debug transport: PSES is language service only");
+                return null;
+            }
+
             if (Stdio)
             {
                 if (DebugServiceOnly)