ART: Clean up #includes in jit_code_cache.h .

And fix code that relied on those indirect #includes.

Also remove forward declaration of art::LinkerPatch because
we actually use art::linker::LinkerPatch.

Test: m test-art-host-gtest
Test: testrunner.py --host --optimizing
Bug: 65574695
Change-Id: I102affed9a3eacbd21b79c370fbc72b5fc762c96