support supercluster#244 arrayType option within cluster sources

[andrewharvey]

At high clusterMaxZoom values and low clusterRadius values with data very close together, the default supercluster Float32Array type starts causing some features to cluster when they shouldn't based on your set clusterRadius.

To resolve this I've exposed an option on cluster sources to set the supercluster type to Float64Array.

I've posted this PR as a WIP for now as I don't think we should actually expose this option like this. I'm thinking we should try to determine based on the clusterMaxZoom and clusterRadius set that (we we just assume there will be very close data present) if Float32Array would suffice or if we need Float64Array and set it transparently.

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