Update the logic for inheriting dexopt artifacts during inherit install.

The old code path assumes that the oat dir is in the following
hierarchy:

oat/
  <isa-1>/
    <filename-1>
    <filename-2>
    ...
  <isa-2>/
    ...

where <isa-*> are supported instruction sets.

At the time of writing, this assumption is true, but it may not be true
in the future as ART evolves. Besides, the old code path depends on the
InstructionSets class, a class for legacy dexopt, preventing us from
removing it.

The new code path preserves the entire oat dir hierarchy regardless of
the directory names and the depth, and it doesn't depend on
InstructionSets.

Bug: 258223472
Test: -
  1. Install a base APK using `adb install`.
  2. Check the files in the oat dir and their inodes.
  3. Install a split APK using `adb install -p` (inherit install).
  4. Verify that the existing files are there in the oat dir at the
     destination and their inodes are unchanged.
Flag: android.content.pm.alternative_for_dexopt_cleanup
Change-Id: Id6a7801b9f8bcec4fa81ce4c4543fee560847526