setFilter method for GeoJSONSource

@mourner is already working on this.

Since May 27, 2021.

## Motivation

You can cluster a `GeoJSONSource`, but it's difficult to filter out source data because the layer `filter` expression applies to the clustered features. The `GeoJSONSource` has a `filter` property, but it can only be specified on source initialization.

To paint an illustrative example, let's say we have 50K features with a date property and as a user interacts with our app, we allow them to filter the clustered map to just show features in a certain date range. If the 50K features weren't clustered, we could just apply a `filter` to each layer we wanted to filter. But with the 50K features clustered, we either need to filter the source data ourselves and use `setData` or we need to remove the source and add it back with a `filter` applied to it. The former requires source data regeneration on our end, and the latter results in a flash as the map removes all features from the old source and adds all features from the new source.

Thanks for your consideration, and also open to alternative ideas! ❤️

## Design Alternatives

Would it be possible to add a `setFilter` method to a `GeoJSONSource` to allow for this workflow?

## Design

Currently, it looks like the `setData` workflow in a `geojson_source` will kick off a `loadData`, which checks to see if there is a filter, and if so, does a `data.features.filter`. Since this `setData` workflow looks at the `filter`, it seems like `setFilter` could potentially be a subset of this workflow.

### Mock-Up

### Concepts

### Implementation