Figure out the reply to "PlanExplainsStop" once when we stop and then use the cached
value.  This fixes problems, for instance, with the StepRange plans, where they know that
they explained the stop because they were at their "run to here" breakpoint, then deleted
that breakpoint, so when they got asked again, doh!  I had done this for a couple of plans
in an ad hoc fashion, this just formalizes it.

Also add a "ResumeRequested" in Process so that the code in the completion handlers can
tell the ShouldStop logic they want to resume rather than just directly resuming.  That allows
us to handle resuming in a more controlled fashion.

Also, SetPublicState can take a "restarted" flag, so that it doesn't drop the run lock when
the target was immediately restarted.
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M    test/lang/objc/objc-dynamic-value/TestObjCDynamicValue.py
M    include/lldb/Target/ThreadList.h
M    include/lldb/Target/ThreadPlanStepOut.h
M    include/lldb/Target/Thread.h
M    include/lldb/Target/ThreadPlanBase.h
M    include/lldb/Target/ThreadPlanStepThrough.h
M    include/lldb/Target/ThreadPlanStepInstruction.h
M    include/lldb/Target/ThreadPlanStepInRange.h
M    include/lldb/Target/ThreadPlanStepOverBreakpoint.h
M    include/lldb/Target/ThreadPlanStepUntil.h
M    include/lldb/Target/StopInfo.h
M    include/lldb/Target/Process.h
M    include/lldb/Target/ThreadPlanRunToAddress.h
M    include/lldb/Target/ThreadPlan.h
M    include/lldb/Target/ThreadPlanCallFunction.h
M    include/lldb/Target/ThreadPlanStepOverRange.h
M    source/Plugins/LanguageRuntime/ObjC/AppleObjCRuntime/AppleThreadPlanStepThroughObjCTrampoline.h
M    source/Plugins/LanguageRuntime/ObjC/AppleObjCRuntime/AppleThreadPlanStepThroughObjCTrampoline.cpp
M    source/Target/StopInfo.cpp
M    source/Target/Process.cpp
M    source/Target/ThreadPlanRunToAddress.cpp
M    source/Target/ThreadPlan.cpp
M    source/Target/ThreadPlanCallFunction.cpp
M    source/Target/ThreadPlanStepOverRange.cpp
M    source/Target/ThreadList.cpp
M    source/Target/ThreadPlanStepOut.cpp
M    source/Target/Thread.cpp
M    source/Target/ThreadPlanBase.cpp
M    source/Target/ThreadPlanStepThrough.cpp
M    source/Target/ThreadPlanStepInstruction.cpp
M    source/Target/ThreadPlanStepInRange.cpp
M    source/Target/ThreadPlanStepOverBreakpoint.cpp
M    source/Target/ThreadPlanStepUntil.cpp
M    lldb.xcodeproj/xcshareddata/xcschemes/Run Testsuite.xcscheme