Recursive window thumbnails would look awesome on the screen, but reality
is that X/OpenGL or $DEITY doesn't like it at all and decided to just
freeze the view.
So let's delay all the redirecting till the WindowThumbnail has been
added to its QQuickWindow and if the window id is the one of the own
window we just render the icon instead.
New qquick item in PlasmaCore to render a live updating window
thumbnail. The implementation uses XCB to redirect the specified
window using the composite extension. This means a running compositor
is not required. Through the damage extension the item tracks changes
to the window and triggers updates of the texture. Furthermore the
item tracks geometry changes of the window to recreate the window
pixmap.
If the pixmap of the window is valid, a texture is generated from it
using the glx texture from pixmap extension. For this a new optional
dependency for glx is added. On platform where glx is not available
(e.g. Windows, Linux with OpenGL ES) this will not get compiled and
the window's icon is used instead as a fallback.
REVIEW: 112142
