Add multiple specialization constants to Forward+ and Mobile.

[DarioSamo]

Since #90400 is now merged, it is now possible for us to further specialize shaders without adding stutters when the configuration of the scene changes.

I turned the following dynamic attributes of the shader into specialization constants and got some measurable improvements in frame time already. Most of these specializations are focused on the mobile renderer.

• Omni light count
• Spot light count
• Directional light count
• Reflection probe count
• Multimesh format
• Ambient cubemap toggle
• Reflection cubemap toggle
• Scene roughness limiter

TPS Demo from here

Average GPU Time in Mali-G78

• master: 31.2ms
• mobile-scs: 28.6ms

Further improvements could be found as I dig deeper into the shader for more optimization opportunities.

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Contributed by W4 Games. 🍀

[clayjohn]

Looks fantastic, I am very happy that we could finally do this.

[clayjohn]

For future reference for others, these are the low hanging fruit optimizations we can do with spec constants. In the future, we can continue to investigate what other areas would benefit from specializations.

[Repiteo]

Thanks!