Fix up dex cache strings stored in classes

Previously we left the image pointer instead of fixing up the pointer
to the one in the BSS. This only showed up because JIT does the same
as boot image, bypassing null check.

Fixed a bug where oat files without embedded dex cache arrays would
get their dex cache arrays corrupted.

Added a non virtual class visitor for performance.

Bug: 26846419
Bug: 22858531

Change-Id: I8cd0d61e440f753b4628ddb8c932eb23a0a81027