Merge pull request #4976 from comex/poll-events

Overhaul EmuWindow::PollEvents to fix yuzu-cmd calling SDL_PollEvents off main thread

src/yuzu/bootmanager.cpp

@@ -314,7 +314,7 @@ GRenderWindow::~GRenderWindow() {
     input_subsystem->Shutdown();
 }
 
-void GRenderWindow::PollEvents() {
+void GRenderWindow::OnFrameDisplayed() {
     if (!first_frame) {
         first_frame = true;
         emit FirstFrameDisplayed();