Port of java.io.F* classes from openJdk8

- Cosmetic javadoc/generic changes.
- Added android-changed marker to FileDescriptor.
- File(Input|Output)Stream native open is wrapped
to allow instrumentation.
- FilenameFilter, FileFilter are @FunctionalInterface.
- Removed unused FileSystem#getFileSystem method.

Test: cts run of CtsLibcoreTestCases
Bug: 31237296
Change-Id: I4ff062f35c1ecba26b5c6833d818c8ccafae447d