Fix JDWP Virtualmachine.Resume command

We used to call ThreadList::UndoDebuggerSuspensions but this is not
correct. Indeed Virtualmachine.Resume command should be performed
as many times as all threads have been suspended (either by the
Virtualmachine.Suspend command or the application of suspend policy
ALL for event).

This CL fixes this issue by adding ThreadList::ResumeAllForDebugger.
It decrements suspend count and debug suspend count by 1 (globally
and for each thread).

It also handles the case where Virtualmachine.Resume is called while
threads have not been suspended (global debug suspend count is 0). In
this case we just print a warning and do nothing.

Bug: 17974047

(cherry picked from commit 253fa555)

Change-Id: I38b38240f84f141670506e88fa5c2480f856fdd6