Fix addLayer() typing to allow adding a source with a layer

[neodescis]

Closes #2442.

Tweaks the typing for map.addLayer() and style.addLayer() to allow adding a source with the layer.

Launch Checklist

• Confirm your changes do not include backports from Mapbox projects (unless with compliant license) - if you are not sure about this, please ask!
• Briefly describe the changes in this PR.
• Link to related issues.
• Include before/after visuals or gifs if this PR includes visual changes.
• Write tests for all new functionality.
• Document any changes to public APIs.
• Post benchmark scores.
• Add an entry to CHANGELOG.md under the ## main section.

[HarelM]

Adde some nit picking, otherwise looks good.

[neodescis]

Nit picking appreciated. I added a changelog entry as well.

[HarelM]

There are still lint warning... Can you fix those?

[neodescis]

Sorry, missed removing imports after consolidating the type to AddLayerObject. Should be fixed now.