TestTagMarker
Marker element that holds a TestTag for identification in test and preview environments.
This marker element is used internally by the testTag extension function to attach a TestTag to a Marker that will be passed to query, mutation, or subscription operations.
The TestTagMarker allows the client implementation to identify the operation by its TestTag rather than its ID, which is particularly useful when dealing with auto-generated IDs that might change during configuration changes or recompositions.