Make ArtMethod methods const or requiring the mutator lock.

Helps the jitzygote optimization on sharing the boot image methods
post fork.

The CL shows that the code base already almost fully handles requiring
the mutator lock when mutating ArtMethod data.

Bug: 119800099
Test: builds
Change-Id: If4a938b66aac85304ec0a27c53bb9fa951191d8c
5 files changed