examples/windowsize: FPS is too low on fullscreen on macOS about ebiten

[hajimehoshi]

Apparently, the freezing issue was already fixed, but the app is still very heavy. I'm investigating this now.

EDIT: The freezing issue was #2847

[hajimehoshi]

I could reproduce this:

1. Run go run examples/windowsize
2. Press R to make the window resizable , and press U to set the app to be suspended when unfocused
3. Make the window fullscreen
4. Switch the focus back and forth

[hajimehoshi]

Changing 2 to 3 at SetMaximumDrawableCount in internal/graphicsdriver/metal fixed the issue, but why...?

[hajimehoshi]

Interestingly, this issue doesn't occur when fullscreeing by pressing F. This happens when fullscreening by pressing a green button.