ART: Refactor known-classloader visits

Refactor visiting dex Elements and DexFiles in known classloaders,
unifying the walking code.

Test: m test-art-host
Bug: 74410240

(cherry picked from commit b8e7c370ccfc53cca8c7caeee7535693668f70fe)

Change-Id: I20552b1979f0d4ce44717baca21bad26bb02d6bc
Merged-In: I4203ac4fbb0ee68660aadc0dfbf8affacbc03b8b
4 files changed