Passage knows its own docID [LUCENE-5181]

The new PostingsHighlight package allows for retrieval of term matches from a query if one creates a class that extends PassageFormatter and overrides format(). However, class Passage does not have a docID field, nor is this provided via PassageFormatter.format(). Therefore, it's very difficult to know which Document contains a given Passage.

It would suffice for PassageFormatter.format() to be passed the docID as a parameter. From the code in PostingsHighlight, this seems like it would be easy.

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Migrated from [LUCENE-5181](https://issues.apache.org/jira/browse/LUCENE-5181) by Jon Stewart, updated Aug 26 2013

Start by reading the PostingsHighlight package, especially Passage and PassageFormatter.format(), to trace how passages are created and formatted. Determine how the document ID should reach the formatter, then update the relevant tests so formatting can verify the ID is available.

Written by the indexing model from the issue text.