Assorted fixes for bugs in the PagedBytesReference tests, plus a typo
where the wrong variable was used for a calculation.

Closes #5549
[DOCS] fixed typo

Closes #5272
[TEST] Increase logging on MinDocCountTests.
Convert TermQuery to PrefixQuery if PHRASE_PREFIX is set

We miss to add a single term to a prefix query if the query in only a
single term.

Closes #5551