Support DOTS Instancing in a a custom shader

To support DOTS Instancing, a shader needs to do the following:

• Use shader model 4.5 or newer. Specify #pragma target 4.5 or higher.
• Support the DOTS_INSTANCING_ON keyword. Declare this with #pragma multi_compile _ DOTS_INSTANCING_ON.
• Declare at least one block of DOTS Instanced properties each of which has least one property. For more information, see Declaring DOTS Instanced properties.

Note: Shader Graphs and shaders that Unity provides in URP and HDRP support DOTS Instancing.