Implement == and hashCode in MapCamera

This will ensure assertions like the one described in [this issue](fleaflet#1613)
work as intended.

lib/src/map/camera/camera.dart

@@ -361,4 +361,19 @@ class MapCamera {
     final newCenter = unproject(mapCenter + newOffset);
     return newCenter;
   }
+
+  @override
+  int get hashCode => Object.hash(
+      crs, minZoom, maxZoom, center, zoom, rotation, nonRotatedSize);
+
+  @override
+  bool operator ==(Object other) =>
+      other is MapCamera &&
+      other.crs == crs &&
+      other.minZoom == minZoom &&
+      other.maxZoom == maxZoom &&
+      other.center == center &&
+      other.zoom == zoom &&
+      other.rotation == rotation &&
+      other.nonRotatedSize == nonRotatedSize;
 }