[Keyboard Manager] Allow whitespace-only TextRemappings (#46510)

Title.

Closes #46453

src/modules/keyboardmanager/KeyboardManagerEditorUI/Helpers/ValidationHelper.cs

@@ -90,7 +90,7 @@ namespace KeyboardManagerEditorUI.Helpers
                 return ValidationErrorType.EmptyOriginalKeys;
             }
 
-            if (string.IsNullOrWhiteSpace(textContent))
+            if (string.IsNullOrEmpty(textContent))
             {
                 return ValidationErrorType.EmptyTargetText;
             }