Change LatLonShape encoding to use selective indexing [LUCENE-8521]

#9542 allows for selecting the first n dimensions to be used for building the index and the remaining dimensions to be used as data dimensions. This feature changes `LatLonShape` encoding to a 7 dimension encoding instead of 6; where the first 4 are index dimensions defining the bounding box of the `LatLonShape.Triangle` and the remaining 3 data dimensions defining the vertices of the triangle.

---
Migrated from [LUCENE-8521](https://issues.apache.org/jira/browse/LUCENE-8521) by Nick Knize (@nknize), updated Oct 22 2018
Attachments: [LUCENE-8521.patch](https://apache.github.io/lucene-jira-archive/attachments/LUCENE-8521/LUCENE-8521.patch)

Start with the LatLonShape encoding and LatLonShape.Triangle entry points described in the issue, then read issue #9542 and the attached LUCENE-8521.patch for the selective-indexing context. Done means the encoding uses seven dimensions: four index dimensions for the triangle bounding box and three data dimensions for its vertices.

Written by the indexing model from the issue text.