cheets: Delegate openAppFuseFile operation to vold

Relanding this since it fails to be merged on ag/5521120 (blocked by
Presubmit, seems to be caused by temporary state) - this one now
passes presubmit without any changes.

Bug: 72017414, 110379912
Test: testOpenProxyFileDescriptor passes

Change-Id: I6e0302e9f043836857e16bbe76d4bb927ccae784