[api-minor] Allow specifying an extra-delay, in RenderTask.cancel, for worker-thread aborting of operatorList parsing

This is done to support upcoming viewer-changes, and in order to prevent third-party users from outright breaking things we'll simply ignore too large values.

test/unit/api_spec.js

@@ -2870,6 +2870,7 @@ Caron Broadcasting, Inc., an Ohio corporation (“Lessee”).`)
         expect(reason instanceof RenderingCancelledException).toEqual(true);
         expect(reason.message).toEqual("Rendering cancelled, page 1");
         expect(reason.type).toEqual("canvas");
+        expect(reason.extraDelay).toEqual(0);
       }
 
       CanvasFactory.destroy(canvasAndCtx);