Port last remaining java.io changes in openJdk8

- Added missing Android-changed markers in UnixFileSystem and
canonicalize implementation
- JNU_ClassString caching in UnixFileSystem_list0 native method
- Port of changeset 6785:ef0c60b93a17, "Remove use of JVM_* functions from java.io code":
 * Removes use of JVM__NativePath
 * Introduces handleOpen method (which handles properly the
   open with EISDIR, we can remove android fix for it)

Bug: 31237296
Test: cts run of CtsLibcoreTestCases
Change-Id: I57bd24aef29cf7d9563f0cc36dde712f232a9255