Perf improvement: Don't union features iteratively with locationReducer

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I made this change in 86ab4ae

In the past, Turf/JSTS/martinez could not easily handle aggregated features, so we'd iteratively union them all together with the _locationReducer function. (this was slow)

Now mfogel/polygon-clipping can handle multiple input coord arrays, so we can send all the coords in one shot and it just works fast

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Side by side comparison - It's really a lot faster now!