fix random number generation used for spatial tests [LUCENE-7185]

The current method is not very good for testing.

- It will only rarely or never return edge cases like -180/180/-90/90
- It will only rarely return 0
- There are many possible doubles within the ranges (-180..180/-90..90) it will never return

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Migrated from [LUCENE-7185](https://issues.apache.org/jira/browse/LUCENE-7185) by Robert Muir (@rmuir), updated Apr 18 2016
Attachments: [LUCENE-7185_polygon.patch](https://apache.github.io/lucene-jira-archive/attachments/LUCENE-7185/LUCENE-7185_polygon.patch), [LUCENE-7185_sorting.patch](https://apache.github.io/lucene-jira-archive/attachments/LUCENE-7185/LUCENE-7185_sorting.patch), [LUCENE-7185.patch](https://apache.github.io/lucene-jira-archive/attachments/LUCENE-7185/LUCENE-7185.patch), [newRandom.png](https://apache.github.io/lucene-jira-archive/attachments/LUCENE-7185/newRandom.png), [oldRandom.png](https://apache.github.io/lucene-jira-archive/attachments/LUCENE-7185/oldRandom.png)

Start by reviewing the attached LUCENE-7185.patch, LUCENE-7185_polygon.patch, LUCENE-7185_sorting.patch, and the newRandom.png/oldRandom.png comparisons to locate the spatial-test random-number method. Done means the generator can produce boundary values, zero, and a broader range of doubles within the longitude and latitude limits.

Written by the indexing model from the issue text.