FastVectorHighlighter Overlapping Queries Do Not Highlight [LUCENE-7593]

Example Text:
ABCDEF

Example Query:
AB or ABC

I got two terms hit, (AB, startOffset=0, endOffset=2, weight=4), (ABC, startOffset=0, endOffset=3, weight=5), in FieldPhraseList's constructor, line 103, addIfNoOverlap, only (AB) were highlighted, and (ABC) with higher weight had been dropped because offset overlapping

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Migrated from [LUCENE-7593](https://issues.apache.org/jira/browse/LUCENE-7593) by Luo Ji, updated Mar 07 2018

Start in FieldPhraseList's constructor at addIfNoOverlap, which the report identifies as dropping the overlapping ABC term after AB is accepted. Reproduce the AB or ABC example against ABCDEF and verify that the higher-weight overlapping match is highlighted rather than discarded.

Written by the indexing model from the issue text.