OatFileAssistant: look at vdex file for IsDexOptNeeded

OatFileAssistant: look at vdex file for IsDexOptNeeded

Even if the oat file cannot be opened, there may be a vdex file that
contains valid dex code. The oat file assistant should take this into
account when determining the dexopt status.

Bug: 34339100
Test: oat_file_assistant_test, with new tests added.
Test: install an app, dumpsys package to show app status,
      delete app's oat file, dumpsys package to show status as vdex only,
      cmd package compile -r install app, verify in log that input vdex fd is
      provided to dex2oat.

Change-Id: Iab43e617a899773b318d61adeb117ed2cec085da