Side affects in some fullscreen apps

[derpmacos]

In 10.1.4.2 this causes a fullscreen frontmost window (a manually created NSWindow with frame matching NSScreen frame) with a MTKView (i.e. in another app!) to stop updating whilst this app is running.

Further investigation required, notably:

• does this affect every fullscreen frontmost window?
• can we detect the windows that cause the issue?
• can we draw the problematic windows another way (and still be performant)?

Note: Our suspicion is that Apple does something 'interesting' with respect to fullscreen windows in the name of performance...

[derpmacos]

A fullscreen NSWindow containing a NSOpenGLView was not affected.