graphics: stall waitUntilSafeForRendering in its command processor instead of the GPU thread

src/graphics/presentation/videoOut.h

@@ -38,7 +38,7 @@ public:
 	void CompleteFlip(uint64_t request_id);
 	void SubmitFlipPreparation(uint64_t request_id);
 	void WaitForSubmitSlot(int handle);
-	void WaitFlipDone(int handle, int index);
+	[[nodiscard]] bool IsSafeForRendering(int handle, int index);
 
 	[[nodiscard]] Impl& State() noexcept;