Separate render scale slider for glass cockpit screens

[CptLucky8]

@smitty9792

the screens can be difficult to see while still having a decent FPS. Meanwhile, the floating VFR Map panel can be shown in excellent clarity at the same time that VR render scale is turned down.

This is exactly why I’m suggesting to use the VR Overlays to rendering EFIS screens:
EFIS Screens Problems and Solutions for higher legibility