Desktop image protocol

Inochi2D is currently working on a UI rewrite that is based off of the Microsoft Windows Fluent design.

The Mica style involves taking the background, specifically a portion for the Mica Alt design, and blurring it. Wayland allows applications to have transparent areas, however there is no protocol for blurring portions of a window (there is !43, however it specifies that the compositor decides how windows are blurred. This isn't desired in this case).

For the main Mica design, it seems to use the main color of the background, however that could probably be done with the help of the accent color portal.

A protocol that gives applications a portion of the background that the application is sitting on would work to allow application designs such as this. Alternatively, the whole background can be sent and a portion of it told to be used.