Also fixed DarwinEQEnqueue to match changes to the callback
And also use dpmsstubs.c rather than copying the code into darwin.c
(cherry picked from commit 4c5c30a4beb7a427b00b18097f548876ad3c11d7)
Leaving xpr unflattened since we want modularity to replace that with xpc (XPluginComposite) at some point
(cherry picked from commit 48e6a75fbdd0fee86e364f02ace83f20b312a2b2)