Port MergeQueue performance improvements from GeoTrellis

[metasim]

GeoTrellis commits locationtech/geotrellis@da3b299 through locationtech/geotrellis@00fa464 include performance improvements in cases in that project's copy of MergeQueue that would likely benefit users of this library.

Relevant GT issues

• MergeQueue is slow for some query range sets geotrellis#2358
• Allow Merge Queue To Handle Larger Inputs geotrellis#2400

Relevant Gitter dialog

• https://gitter.im/geotrellis/geotrellis?at=59b16d03614889d475cf39b1
• https://gitter.im/geotrellis/geotrellis?at=59b18df44e50cfde27152b69
• https://gitter.im/geotrellis/geotrellis?at=59b18173b16f264642177329

Benchmarks

A benchmark rig comparing it against a simple Scala collections version are found here. The results are discussed here:

• JMH Prototype  geotrellis#2365 (comment)