Add new matcher to check output file content for WordCountIT and WindowedWordCountIT

[kennknowles]

Test use case like #4755 (comment) shows that verify lines of output for integration test makes the validation and debugging easier than simple verify checksum. We'd like to add a new matcher (like FileContentMatcher) to very lines given expected files.

This matcher can be applied to ITs that already use FileChecksumMatcher (etc. WordCountIT and WindowedWordCountIT).

Imported from Jira BEAM-3810. Original Jira may contain additional context.
Reported by: markflyhigh.