Differentiate within/approx SpatialPrefixTree leaf cells [LUCENE-6362]

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This patch enables indexed cells to be differentiated between those that are completely within the shape that was indexed, and those on the edge (intersects, not within) but reached a precision threshold. The point of this differentiation is to be used by the two-phase optimized predicates in #6641 to be able to avoid an expensive geometry check for accuracy, in more cases than it is able to without this differentiation. In particular, if the query shape is within an indexed shape, then this cell differentiation will enable a predicate to observe that without doing a geometry check.

note: patch here is moved from #6641 as this is really an add-on

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Migrated from LUCENE-6362 by David Smiley (@dsmiley)
Attachments: LUCENE-6362 SPT leaf differentiate.patch
Linked issues:

• Spatial, enhance RPT to differentiate confirmed from non-confirmed hits, then validate with SDV [LUCENE-5579] #6641

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David Smiley (@dsmiley) (migrated from JIRA)

Here's the patch; a bit further along than it's original form posted #6641. I think all it needs is a test or two, maybe. But I think this issue overall should wait until #6641 as that will make this easier to test and of course we can observe the benefit to this cell differentiation that we trade-off in index size and some complexity.