Bug 1621762: Part 4 - Move some code from ProducerConsumerQueue.h to QueueParamTraits.h r=jgilbert

Move QueueParamTraits, which are common between PCQ and IpdlQueue, to a file they both include.  This also changes the namespace of a handful of the classes, like the Marshaller.

Differential Revision: https://phabricator.services.mozilla.com/D68260

dom/canvas/moz.build

@@ -60,6 +60,7 @@ EXPORTS.mozilla.dom += [
     'ImageUtils.h',
     'OffscreenCanvas.h',
     'ProducerConsumerQueue.h',
+    'QueueParamTraits.h',
     'TextMetrics.h',
     'WebGLChild.h',
     'WebGLCommandQueue.h',