Add File.java to forbidden APIs

This commit cuts over all of core (not quite all tests) to java.nio.Path
It also adds the file class to the core forbidden APIs to prevent its usage
Can we add all the java.io.File signatures (even with ones commented out if we can't yet fix them).

Full list here: http://svn.apache.org/repos/asf/lucene/dev/trunk/lucene/tools/forbiddenApis/lucene.txt