This is to avoid false positives.
By default files are large if uncompressed size > 10 MB. Only configurable internally.
Also add auto tests.
Task-number: QTBUG-91392
Pick-to: 6.0 6.1
Change-Id: I32258cb7c957f2a23a05157ba4ed5c0af2ba585e
Reviewed-by: Mårten Nordheim <marten.nordheim@qt.io>
Reviewed-by: Edward Welbourne <edward.welbourne@qt.io>