Support basemap sessions for basemap layers

### Describe the problem

The basemap styles service recently published basemap sessions for ArcGIS Location Platform accounts. These session tokens can already be used to authenticate requests with `VectorBasemapLayer`, but there is additional functionality that would be gained by allowing the entire session to be passed.

### Describe the proposed solution

The new Maplibre ArcGIS plugin already supports this via the `BasemapSession` class: https://github.com/Esri/maplibre-arcgis/blob/main/src/BasemapSession.ts

I would like to see similar functionality implemented for use with Esri Leaflet.

### Alternatives considered

I'm not sure if this session class should live in this repository, or elsewhere, but it would be intended for use expressly with `VectorBasemapLayer`.

### Additional Information

_No response_

Start by inspecting the VectorBasemapLayer implementation and comparing the linked maplibre-arcgis src/BasemapSession.ts class. Determine where a basemap session should live in this repository and how it should be passed to VectorBasemapLayer; done means the full session can authenticate the layer rather than only a session token.

Written by the indexing model from the issue text.