Preverify InMemoryDexClassLoader-loaded classes from vdex

This patch creates a new subclass of OatFile - OatFileBackedByVdex -
which initializes OatDexClass instances using the verification info in
a vdex file created by a previous instance of the class loader.
The OatFile is not backed by an actual .oat file.

Bug: 72131483
Test: art/tools/run-libcore-tests.sh
Test: art/test.py -b -r -t 692 -t 693
Change-Id: I3fd055abe17ee9739c07f2e2f4fc2543e4ec8c9e