GE Debugger: Add separate step based on vsync.

I think there were some games where this would step in the middle of a
frame, but not seeing it commonly now.  So make it the default, but allow
both methods in the menu.

Fixes #15893.

GPU/Debugger/Debugger.cpp

@@ -154,6 +154,15 @@ void NotifyDisplay(u32 framebuf, u32 stride, int format) {
 	}
 }
 
+void NotifyBeginFrame() {
+	if (!active)
+		return;
+	if (breakNext == BreakNext::VSYNC) {
+		// Just start stepping as soon as we can once the vblank finishes.
+		breakNext = BreakNext::OP;
+	}
+}
+
 int PrimsThisFrame() {
 	return primsThisFrame;
 }