Map default range for IOR Node Socket

The IOR ("Index of Refraction") node socket should be re-mapped, so that the default values reflect reality. Currently, scrubbing through the node socket's value with the mouse, the value range is about 1-100.

In physics, the IOR value of all known natural materials does not exceed 5. Synthetic materials have been documented going as high as ~40.

Practically, users need to adjust the IOR value from 1.0 (vacuum) to 4.0 (Germanium) for 99% of materials. The tooltip says as much. Mapping this as the default range for this socket will allow for greater speed and accuracy while dialing in shader properties.

There's an argument to be made for IOR to be a mapped slider from 1.0 to 4.0, with allowance for input override.