Box projection for reflection probes

Original issue: https://github.com/microsoft/MixedRealityToolkit-Unity/issues/9150

Describe the problem

Box projection doesn't seem to work on the MRTK standard shaders, which causes really bad reflective surfaces for head mounted displays (especially in rooms)

Describe the solution you'd like

Enable box projection for reflection probes to work with the MRTK standard shader

Describe alternatives you've considered

Writing some custom shader

Additional context

the MRTK/Standard shader does not account for box projection (or reflection probe blending). We should call this out in the docs.

To properly support box projection we need to introduce a call to the BoxProjectedCubemapDirection method within UnityStandardUtils. There is a great example of the changes need on this page: https://catlikecoding.com/unity/tutorials/rendering/part-8/

Thanks @Cameron-Micka I tweaked the shader so the worldReflection parameter reads as follows:

float3 worldReflection = BoxProjectedCubemapDirection(reflect(incident, worldNormal), i.worldPosition, unity_SpecCube0_ProbePosition, unity_SpecCube0_BoxMin, unity_SpecCube0_BoxMax);

I didn't add blending as I didn't need it (yet), so this does the trick so far

Start by locating the MRTK standard shader and its use of UnityStandardUtils, then compare the reflection-probe path with the BoxProjectedCubemapDirection example linked in the issue. Done means box projection works for reflection probes in the MRTK standard shader, with the relevant shader behavior verified on reflective surfaces.