Remove FieldMaskingSpanQuery (or fix its scoring) [LUCENE-3723]

In Lucene 4.0 we added new scoring mechanisms, but FieldMaskingSpanQuery is a serious problem:

Because it lies about the fields of its terms, this sometimes results in totally bogus
statistics, cases where a single terms totalTermFreq exceeds sumTotalTermFreq for the entire field (since its lying about it).

Such lying could result in NaN/Inf/Negative scores, exceptions, divide by zero, and other problems,
because the statistics are impossibly bogus.

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Migrated from [LUCENE-3723](https://issues.apache.org/jira/browse/LUCENE-3723) by Robert Muir (@rmuir)
Attachments: [LUCENE-3723_test.patch](https://apache.github.io/lucene-jira-archive/attachments/LUCENE-3723/LUCENE-3723_test.patch), [LUCENE-3723.patch](https://apache.github.io/lucene-jira-archive/attachments/LUCENE-3723/LUCENE-3723.patch)

Start by reading the FieldMaskingSpanQuery implementation and the attached LUCENE-3723_test.patch. Investigate how its field reporting produces inconsistent term statistics and can lead to invalid scores; done means either removing the query or correcting its scoring so these impossible statistics and resulting failures no longer occur.

Written by the indexing model from the issue text.