[DexLoadReporter] Report classloader contexts directly from classloader

At the moment classloader contexts are incorrectly computed in the
PackageManager for secondary dex files. There are two issues:

(1) The wrong computed classLoaderContext will be reported for a secondary
    dex file if it was loaded at the same time as a primary dex file
    - This is due to the continue statement that doesn't increment
      dexPathIndex
(2) If a secondary dex file was loaded with a shared library then that
    shared library info isn't passed through the dex load reporting
    infrastructure, and thus its classloader context is incorrectly computed
    in PackageManager.

In order to fix the issues described above & prevent further classloader
context computation divergences between the package manager and the
runtime, lets compute the classloader context in the runtime at dex load
time and report the expected classloader context directly to
DexLoadReporter (and thus the package manager).

Notes: This is mostly just a refactor (i.e. there are a lot of line
changes, but functionally speaking this set of CLs doesn't do much
except change where the classloader context is computed)

Addendum: The bugs described above could also be fixed by:
- changing DexLoadReporter to report information about shared libraries that
  the reported classloaders depend on to PackageManager
- Teach DexoptUtils.processContextForDexLoad about shared libraries
- Fix dexPathIndex calculation in DexManager

I opted for this set of changes instead because this reduces the
possibility of context computation divergence between the framework and the
runtime. Additionally it feels more "solid" that the classloader context
is now computed directly when a dex file is loaded, rather than the
context recreated later on in the PackageManager.

Test: atest com.android.server.pm.dex.DexManagerTests
Test: atest com.android.server.pm.PackageManagerServiceTest
Test: Install app depending on shared library & uses secondary dex
files; adb shell pm bg-dexopt-job; launch app and see odex file
successfully loaded (from smaps/no logcat errors)

Bug: 148494302
Change-Id: I00357cfe086ff149f92c1078c6df6daa713c8f7c