ART: Change lock dumping

Return dex registers as well as dex PCs from FindLocksAtDexPc.

It is necessary to return the registers as the register used for
a monitor-enter operation may be aliased and overwritten by the
time the requested dex PC is reached.

It is at this point necessary to return a set of registers as
optimizations may have eliminated dead registers, and the verifier
has no notion of liveness.

A client of FindLocksAtDexPc should not assume that all registers
can be successfully retrieved from a stack frame, with the possibility
of none. Only a properly verified method (i.e., lock verification succeeded)
implies that at least one register should work for all locks held at
any point in the program.

Bug: 68703210
Test: art/test/testrunner/testrunner.py -b --host -t 167
Change-Id: I9027787e395cf8df0e7699a606665edb2ecb5136