JVMTI set & get local variables

Basic implementation of the JVMTI can_access_local_variables
capability. This implements the functions and behaviors required for
this capability.

Currently enabling this capability immediately forces all threads to
use the interpreter exclusively. This behavior should be removed
eventually.

Tests follow in next CL.

Test: ./test.py --host -j50
Bug: 34414073
Bug: 36892980
Change-Id: I11a4d3cb2b945955cca270efdee2fbfd2601e0ba