Assign non-runtime /apex/* dex files to platform domain

Until now only /system/framework and /apex/com.android.runtime were
known locations, assigning "platform" domain to the former and
"core-platform" domain to the latter. The media and conscrypt modules
were left in the "application" domain.

This patch adds a hardcoded path to the apex root and assigns all dex
files in subdirectories to the "platform" domain. This affects both
conscrypt and media modules.

Any other dex files on boot classpath are also assigned to "platform"
on first access. A warning is printed in such case and it is now deduped
to avoid logspam.

Bug: 125701194
Bug: 119068555
Test: compiles, boots, no conscrypt/media warnings about missing domain
Test: art/test.py -b -r -t 674
Change-Id: I33bef18459741095d3d99b541fc88b21cf547800