Under wayland we support high DPI putting by putting a separation
between the logical co-ordinate system and the resolution of rendered
assets.
When a window is on a high DPI screen, we should render at the higher
resolution.
Like the window scaling this handles any combination of a 2x scaled
decoration being rendered on a 1x screen or vice versa.
This patch is a bit different from the other scaling stuff. We have to
generate the quads *before* we have an updated texture with the new
scale. This means the scale isn't attached to the buffer like elsewhere.
That's why I added a property in TopLevel so there's still one canonical
source and things can't get out of sync.
BUG: 384765