menu: Blanks framebuffer before exiting/launching XBEs.

[abaire]

• Blanks the framebuffer before exiting the dashboard (see discussion in XboxDev/nxdk/#511)
• Adds a bottleneck for activities that exit the dashboard to allow a future loading screen (in prep for Feature: Display a launch image before launching new XBEs #113 )

[GXTX]

I wonder if it would be better to have this fixed upstream. I know there's discussion already going on as to why artifacts happen.

[abaire]

Yup, it's in XboxDev/nxdk/#511 which is where the suggestion to turn off the video output altogether for now came from. The correct fix in the nxdk to allow saving the framebuffer sounds like it'll be be a much larger project.

In my experience memsetting the framebuffer leads to ok results (there's still clearly some corruption but it's not as bad as before the 511 patch) so we could probably do that for now if killing the video ends up having undesired effects.