Stub PopLaunchParameter and implement Buffer C Descriptors reading on hle_ipc (#96)

* Stub PopLaunchParameter and implement Buffer C Descriptors reading

* Address PR feedback

* Ensure we push a u64 not a size_t

* Fix formatting

src/core/hle/ipc_helpers.h

@@ -54,6 +54,10 @@ public:
     unsigned GetCurrentOffset() const {
         return static_cast<unsigned>(index);
     }
+
+    void SetCurrentOffset(unsigned offset) {
+        index = static_cast<ptrdiff_t>(offset);
+    }
 };
 
 class RequestBuilder : public RequestHelperBase {