Refactorings around usage of jfieldID - Make encoding and decoding require the mutator lock, in preparation for next CL. - Store jfieldID instead of ArtField* in jvmti data structures, to avoid needing the mutator lock for certain operations. Test: test.py Bug: 481456995 Flag: EXEMPT PURE_REFACTOR Change-Id: I88950b8d732db805ef23011e3f9557575cca686a