What does this PR do?

This is one part of the material shader refactoring neccesary for RFC 152 (Support for multiple Material-Types in Raytracing Hit Shaders).

This PR adds the field "materialShaderDefines": "BasePBR_Defines.azsli" to the abstract materialtype, that will be included by the materialpipeline - shaders before any other files.

This allows us to define Pipeline-Callbacks, that are provided by the rendering-pipeline, and need a full definition of the material-defined structs and SRGs, but that are used in the material-defined functions.

With these Pipeline-Callback we can somewhat separate the material-functions from the rendering pipeline, which is necessary to use the materials in a raytracing-shader or a deferred pipeline.

Specific example from BasePBR_VertexEval.azsli:

previously:

    // GetObjectToWorldMatrix(uint instanceId) uses either the SceneSrg or the ObjectSrg to get the matrix: 
    // In a raytracing shader we don't have an Object-Srg, and the SceneSrg works differently, so this won't compile.
    // Also instancing will work differently, so likely the instanceId won't work either
    
    float4x4 objectToWorld = GetObjectToWorldMatrix(SV.m_instanceId);
    float4 worldPosition = mul(objectToWorld, float4(position, 1.0));

new:

    // VsSystemValues and GetObjectToWorldMatrix(VsSystemValues  SV) are now declared by the 
    // render-pipeline and opaque to the material shader code.

    float4x4 objectToWorld = GetObjectToWorldMatrix(SV);
    float4 worldPosition = mul(objectToWorld, float4(position, 1.0));

Since i had to change the existing shader - templates, this will break custom materials.
Custom materials that use the Material - canvas will work, but the shader-code needs to be recreated by the MaterialCanvas - Editor.

How was this PR tested?

Make sure all shaders from the engine compile, and everything still looks the same.
Tested with vulkan on windows.