ANDROID: fuse: Add support for d_canonical_path

Allows FUSE to report to inotify that it is acting as a layered filesystem.
The userspace component returns a string representing the location of the
underlying file. If the string cannot be resolved into a path, the top
level path is returned instead.

Rolled in fix from
cad4f67e("ANDROID: fuse: Allocate zeroed memory for canonical path")
Note: I've changed the Change-Id since this was previously present, but
      disappeared at some point.

Bug: 23904372
Bug: 171780975
Test: FileObserverTest and FileObserverTestLegacyPath on cuttlefish
Change-Id: I3d752756adb058ba32b47ec61887a2df98e862db
Signed-off-by: Daniel Rosenberg <drosen@google.com>
Signed-off-by: Alessio Balsini <balsini@google.com>