Fix file-backed checks to use IsUntitled

Agent-Logs-Url: https://github.com/PowerShell/PowerShellEditorServices/sessions/25fb4a4a-04f5-471e-93fa-82a0a9cdcd91

Co-authored-by: JustinGrote <15258962+JustinGrote@users.noreply.github.com>

Author: Copilot

src/PowerShellEditorServices/Services/TextDocument/Handlers/CompletionHandler.cs

@@ -366,7 +366,7 @@ private CompletionItem CreateProviderItemCompletion(
             if (textToBeReplaced.IndexOf(PSScriptRootVariable, StringComparison.OrdinalIgnoreCase) is int variableIndex and not -1
                 && System.IO.Path.GetDirectoryName(scriptFile.FilePath) is string scriptFolder and not ""
                 && completionText.IndexOf(scriptFolder, StringComparison.OrdinalIgnoreCase) is int pathIndex and not -1
-                && !scriptFile.IsInMemory)
+                && !scriptFile.IsUntitled)
             {
                 completionText = completionText
                     .Remove(pathIndex, scriptFolder.Length)

src/PowerShellEditorServices/Services/Workspace/WorkspaceService.cs

@@ -319,7 +319,7 @@ public void CloseFile(ScriptFile scriptFile)
         public string GetRelativePath(ScriptFile scriptFile)
         {
             Uri fileUri = scriptFile.DocumentUri.ToUri();
-            if (!scriptFile.IsInMemory)
+            if (!scriptFile.IsUntitled)
             {
                 // Support calculating out-of-workspace relative paths in the common case of a
                 // single workspace folder. Otherwise try to get the matching folder.