Add a way to SwiftUI Map() to add an UIImage to SourceLayer

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## New Feature

In SwiftUI / Mapbox add a way to set/update an image in ImageSource like

ImageSource(id: sourceId)
.image(someImage)
.coordinates(coords)

## Why

I am using a SwiftUI Map() view with

ImageSource(id: sourceId)
.url(someUrl)
.coordinates(coords)

This works, but I would like to use my own Image cache to update ImageSource.
I can use MapReader, to get the map object and do a

try map.updateImageSource(withId: sourceId, image: someImage)

but this is not very SwiftUI like

Start by tracing the SwiftUI Map() and ImageSource APIs, then compare the existing url-based source flow with MapReader and updateImageSource(withId:image:). Done means SwiftUI can set or update an ImageSource from a cached UIImage while retaining coordinate support and matching the requested usage pattern.

Written by the indexing model from the issue text.