Make OutputFormatAdapter public.

Why do that? This enables the JMH extension to benchmark Java code running as GraalVM native image to reuse the same class when it wants to redirect the output from the process to the JMH output.

This is useful for example when Fibula's PGO integration invokes native image to recreate the binary with the profiling information, see https://github.com/galderz/fibula/commit/20eaf64936ef3e8f77eaed2ac7e8094b57e66a8d