Calling source.serialize().data after dynamic update with updateData() only returns features from most recent update.

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### mapbox-gl-js version

v3.14.0

### Browser and version

Chrome Version 134.0.6998.45 (Official Build) (arm64)

### Expected behavior

When calling `source.updateData()` to add new features to a geojson source, I expect `map.getSource(sourceId).serialize().data` to include the full data for the source.

For example, if the map loads and a source is added with feature id "1", then later `updateData()` adds features "2" and "3", I expect `map.getSource(sourceId).serialize().data` to show a FeatureCollection with feature Ids "1", "2", and "3".

### Actual behavior

Instead, calling `map.getSource(sourceId).serialize().data` on a source recently updated with `updateData()` returns only the feature that were included in the latest update.

So, when adding features with ids "2" and "3" to a source that already included feature with id "1" using `updateData()`, then calling `map.getSource(sourceId).serialize().data` returns only features "2" and "3".

### Link to the demonstration

https://jsbin.com/sidesih/2/

### Steps to trigger the unexpected behavior

Start with a geojson source with some data and dynamic:true. Add data using updateData. Call `map.getSource().serialize().data` and see that only the data added in updateData is returned.

Start by reproducing the behavior in the linked JSBin with a dynamic GeoJSON source, then trace the source's updateData() and serialize() paths in mapbox-gl-js. Verify how the initial data and later updates are represented. Done means serialize().data includes the complete FeatureCollection, including features from both the initial load and subsequent updates.

Written by the indexing model from the issue text.