Deliver the interpreter output of tests to RunTests

[Donach]

RunTests.redirectInterpreterOutput installs a stream so that whatever the tests print
goes to RunTests' own output. That stream never received anything: the output went
straight to System.err, bypassing RunTests entirely. A side effect is that
-compactOutput cannot suppress it either, so it still shows up in CI logs.

Three independent reasons, each fixed here:

• ProgramStateIO shadows the stream. It declares its own private PrintStream outStream and overrides getOutStream/setOutStream on top of ProgramState, which
  already has both. The base implementation forwards the new stream to every registered
  NativesProvider; the override did not, so the providers kept their old stream. The
  field and the two overrides are removed and the base class does the work.

• ReflectionNativeProvider.setOutStream is empty. It is the provider that owns
  OutputProvider, which implements println, BJDebugMsg, DisplayTextToPlayer and the
  other printing natives. Because the setter did nothing, OutputProvider kept its
  default System.err. It now forwards to the OutputProvider instances it holds, and
  OutputProvider gets the corresponding setter.

• The PrintStream has no autoflush. Even with the two fixes above, output sat in the
  8 KB buffer of new PrintStream(os) and was never flushed, so a normal test run
  delivered nothing. It now autoflushes, with an explicit UTF-8 charset on the encoding
  side and the matching new String(bytes, UTF_8) on the decoding side, which also fixes
  non-ASCII output being decoded with the platform default charset.

Effect

Output printed by tests during -runtests now reaches the stream RunTests prints to
(stdout on the CLI) instead of System.err, which is what the redirection was written to
do, and -compactOutput suppresses it as intended.

Tests

RunTestsOutputRedirectTests compiles a package with one passing and one failing test that
both print, and asserts the printed output arrives in RunTests' sink, that
-compactOutput suppresses it, and that the summary and assertion message are unaffected.
interpreterOutputIsRedirected fails on unmodified master and passes with this change;
the full ./gradlew test suite passes.