Move the code which translates a dispatch_qaddr into a
queue name out of ProcessGDBRemote and in to the Platform
plugin, specifically PlatformDarwin.

Also add a Platform method to translate a dispatch_quaddr
to a QueueID, and a Thread::GetQueueID().

I'll add an SBThread::GetQueueID() next.


git-svn-id: https://llvm.org/svn/llvm-project/lldb/trunk@192949 91177308-0d34-0410-b5e6-96231b3b80d8