MappedByteBuffer unmapping on JDK 9+

[ppkarwasz]

Description

The MemoryMappedFileAppender fails to unmap its buffers on JRE 9+: the unmapping code (cf. MemoryMappedFileAppender#unsafeUnmap() requires:

--add-opens java.base/java.nio=ALL-UNNAMED
--add-exports java.base/jdk.internal.ref=ALL-UNNAMED

These two permissions are not given by default.

Since Java 9 the cleaner is accessible through sun.misc.Unsafe#invokeCleaner instead.