clone_items() with item_mapping misses basemap layers

[knoopum]

Describe the bug
When using clone_items with item_mapping on a Web Map with a custom basemap, it fails to update mapped items in the baseMap definition of the clone.

To Reproduce
Create a Web Map that contains a Tile Layer (hosted)/Map Service, and uses the same Tile Layer (hosted)/Map Service as its basemap. Ensure the Tile Layer (hosted)/Map Service is available on both the source and target GIS. Define the mapping of the item IDs from the source and target GIS in item_mapping when calling clone_Items.

For example:

cloned_items = target_gis.content.clone_items(
    items=[source_gis.content.get('web_map_item_id)],
    search_existing_items=False,
    item_mapping = {
        'tile_layer_item_id_on_source_gis': 'tile_layer_item_id_on_target_gis'
    }
)

clone_items does properly apply the item_mapping to the operationalLayers in the Web Map, but does not for the baseMap.

For example, the original Web Map's JSON Data definition contains:

    "operationalLayers": [
        {
            "id": "19d6daf5cc8-layer-216",
            "title": "ESGR 1998 GIS as layer",
            "url": "https://tiles.arcgis.com/tiles/4ezfu5dIwH83BUNL/arcgis/rest/services/ESGR_1998_GIS/MapServer",
            "itemId": "71c5068e7f2c47559ee645f10c712fed",
            "layerType": "ArcGISTiledMapServiceLayer"
        }
    ],
    "baseMap": {
        "baseMapLayers": [
            {
                "id": "19d6d80b60a-layer-56",
                "title": "ESGR 1998 GIS",
                "url": "https://tiles.arcgis.com/tiles/4ezfu5dIwH83BUNL/arcgis/rest/services/ESGR_1998_GIS/MapServer",
                "itemId": "71c5068e7f2c47559ee645f10c712fed",
                "layerType": "ArcGISTiledMapServiceLayer"
            }
        ],
        "title": "ESGR Basemap"
    },

While the cloned Web Map's JSON Data definition shows the item_mapping was successfully applied for occurrences under opeartionalLayers, it was not successful applied under baseMap:

    "operationalLayers": [
        {
            "id": "19d6daf5cc8-layer-216",
            "title": "ESGR 1998 GIS as layer",
            "url": "https://tiles.arcgis.com/tiles/ne8azYNvwFhMEpfh/arcgis/rest/services/ESGR_1998_DELETE/MapServer",
            "itemId": "e5deef62dd514c61b62b8b78790016db",
            "layerType": "ArcGISTiledMapServiceLayer"
        }
    ],
    "baseMap": {
        "baseMapLayers": [
            {
                "id": "19d6d80b60a-layer-56",
                "title": "ESGR 1998 GIS",
                "url": "https://tiles.arcgis.com/tiles/4ezfu5dIwH83BUNL/arcgis/rest/services/ESGR_1998_GIS/MapServer",
                "itemId": "71c5068e7f2c47559ee645f10c712fed",
                "layerType": "ArcGISTiledMapServiceLayer"
            }
        ],
        "title": "ESGR Basemap"
    },

Note that in this example, the Tile Layer (hosted)/Map Service was published on the target GIS with a different title, "ESGR 1998 DELETE", while the on the source GIS it is titled, "ESGR 1998".

Expected behavior
When using item_mapping, the expectation is that it will address all references to an item. So for a Web Map, it should also update items under baseMap, and not just operationalLayers.

Platform (please complete the following information):

• OS: Windows
• Browser: Chrome
• Python API Version: 2.4.3