Refactor and improve imgdiag.

Keep ImgDiagDumper alive for all boot image components.
Check that zygote has boot image at the same addresses
as the app we're comparing against zygote.
Check that the loaded boot image is really clean.
Fix a minor bug when checking array elements.
Add a FIXME note to update the diff logic for ASLR.

Test: imgdiag_test
Bug: 77856493
Change-Id: I3498381912e58dda24eb3312eda6b2c6ca1f12f1