Memory leak while creating layers

[AlexKven]

Currently, when the AddLayer method on LeavletInterop.cs is run, it creates a new DotNetObjectReference and passes that to the JavaScript:

public static ValueTask AddLayer(IJSRuntime jsRuntime, string mapId, Layer layer) =>
    layer switch
    {
        TileLayer tileLayer => jsRuntime.InvokeVoidAsync($"{_BaseObjectContainer}.addTilelayer", mapId, tileLayer, DotNetObjectReference.Create(tileLayer)),
        MbTilesLayer mbTilesLayer => jsRuntime.InvokeVoidAsync($"{_BaseObjectContainer}.addMbTilesLayer", mapId, mbTilesLayer, DotNetObjectReference.Create(mbTilesLayer)),
        ShapefileLayer shapefileLayer => jsRuntime.InvokeVoidAsync($"{_BaseObjectContainer}.addShapefileLayer", mapId, shapefileLayer, DotNetObjectReference.Create(shapefileLayer)),
        Marker marker => jsRuntime.InvokeVoidAsync($"{_BaseObjectContainer}.addMarker", mapId, marker, DotNetObjectReference.Create(marker)),
        Rectangle rectangle => jsRuntime.InvokeVoidAsync($"{_BaseObjectContainer}.addRectangle", mapId, rectangle, DotNetObjectReference.Create(rectangle)),
        Circle circle => jsRuntime.InvokeVoidAsync($"{_BaseObjectContainer}.addCircle", mapId, circle, DotNetObjectReference.Create(circle)),
        Polygon polygon => jsRuntime.InvokeVoidAsync($"{_BaseObjectContainer}.addPolygon", mapId, polygon, DotNetObjectReference.Create(polygon)),
        Polyline polyline => jsRuntime.InvokeVoidAsync($"{_BaseObjectContainer}.addPolyline", mapId, polyline, DotNetObjectReference.Create(polyline)),
        ImageLayer image => jsRuntime.InvokeVoidAsync($"{_BaseObjectContainer}.addImageLayer", mapId, image, DotNetObjectReference.Create(image)),
        GeoJsonDataLayer geo => jsRuntime.InvokeVoidAsync($"{_BaseObjectContainer}.addGeoJsonLayer", mapId, geo, DotNetObjectReference.Create(geo)),
        _ => throw new NotImplementedException($"The layer {typeof(Layer).Name} has not been implemented."),
    };

However, since DotNetObjectReference must be disposed when no longer needed, this is a memory leak, since LeafletInterop doesn't keep track of these references and dispose them when the layer is removed. I will fix this in my PR.

[chucker]

Hmmm, I ran into a "item with same key already exists" exception. I haven't looked into how layer IDs (used as keys here) get generated, but perhaps they get incorrectly reused, or maybe there's a concurrency issue here.