Improve javadoc tool handling of streams.

JDK-8268774 is a minimal fix to ensure that logging messages generate by the tool are written to stderr, not stdout.

The fix could be cleaned up.

Suggestions:
* avoid direct use of `JavadocLog.printRawLines` (make the method private?)
* flatten the ToolEnvironment.notice methods down into `JavadocLog`
* change the use of `notice` methods in Start/etc so that the command-line help is written directly to the std-out stream ... i.e. not via `notice`
* establish a documented convention that error/warning/notice methods all go to the diagnostic writer

Separately, Messages:176 looks questionable for not handling embedded newlines. Right now, it may be OK, because the
current usage does not include embedded newlines,

            reporter.getDiagnosticWriter().println(resources.getText(key, args));