Mouse events during frame update

At the moment the mouse/touch event callbacks are executed immediately on browser detecting those. This makes it hard to fence a logic that depends on those events, as they are fired outside of the application update loop.

Since we (end users) are not subscribing to the window events directly, but listening for the application to tell us when an event happened, the application could fire them at a proper time during the frame update instead, in line with its update logic. We can then use its frameend event as a guarantee that all systems and all inputs have been processed and the application is done updating the frame.

Start by tracing where browser mouse and touch callbacks enter the application and how the frame update loop dispatches application events. Compare the current callback timing with frameend; done means event notifications are delivered during the update loop while frameend remains after all systems and inputs are processed.