GRAYSCALE UI SHADER

Shader to convert UI elements to grayscale.
Supports URP and Built-in render pipelines.

Material Parameters:
- Saturation: Controls how much color is preserved (0 = full grayscale)
- Gain: Multiplies final brightness
- Use Alpha Clip: Enables alpha-based transparency cutoff
- Stencil settings: Comparison, ID, Operation, Read/Write Mask
- Color Mask: Defines which color channels are rendered

Tested on: Windows, Mac, Android
Unity Version: 2022.1+
Support: Turishader@gmail.com