Show [reason=vdex-dm] for oat files backed by vdex in dm only.

To differentiate between OTA and Mainline updates and app installations
as contributors to [status=verify] [reason=vdex] occurrences, we need to
assign them different reason strings. The former will retain
[reason=vdex], while the latter will be modified to [reason=vdex-dm].

Bug: 424802934
Test: atest art_standalone_runtime_tests
Test: -
  1. adb install-multiple --incremental base.apk base.dm
  2. adb shell pm art dump <package-name>
  3. See "[status=verify] [reason=vdex-dm]".
  4. adb shell pm compile -m speed-profile <package-name>
  5. adb shell pm art dump <package-name>
  6. See "[status=speed-profile] [reason=cmdline]".
  7. Install a new ART module.
  8. adb shell pm art dump <package-name>
  9. See "[status=verify] [reason=vdex]".
Flag: EXEMPT log change only
Change-Id: I440828fd85ba0f09869d793e4b79971e73eb6d0c