Move single-step control into thread.

This CL moves single-step control into the Thread structure. This is stored in
Thread::single_step_control_ member. This allows to support single-stepping of
multiple threads at the same time.

Since each thread holds its single-step information, we no longer need to use
the breakpoint lock to support single-stepping. It helps reduce lock contention
on this lock while debugging.

All JDWP tests passed on the host and on the target with this CL.

Bug: 11667502
Change-Id: I886d5c8c625ca5a072803e296c32eec5f7e9e82d
4 files changed