Programmatically remove banding with noise

[Cameron-Micka]

Describe the problem

Banding is present in our texture based iridescence features and gradient features:

Describe the solution you'd like

Would be good to have an option in the GT/Standard and GT/Standard Canvas shaders to remove banding via a technique like this: Removing Banding in Linelight | pixelmager.github.io

Means we can use compressed textures and not worry about banding as much.

Describe alternatives you've considered

Use uncompressed textures or deal with banding.

Additional context

Related to: https://github.com/microsoft/MixedReality-GraphicsTools-Unity/issues/21