Fix terrain artifacts by marking texture index as non-uniform. (#18932)

Closes: https://github.com/o3de/o3de/issues/18924

Signed-off-by: Ross Charles Campbell <[email protected]>

Gems/Terrain/Assets/Shaders/Terrain/TerrainDetailHelpers.azsli

@@ -96,7 +96,7 @@ void AddDetailSurface(inout DetailSurface surface, in DetailSurface surfaceToAdd
 
 float4 SampleTexture(uint index, in MaterialContext materialContext)
 {
-    return Bindless::GetTexture2D(index).SampleGrad(TerrainMaterialSrg::m_detailSampler, materialContext.m_uv, materialContext.m_ddx, materialContext.m_ddy);
+    return Bindless::GetTexture2D(NonUniformResourceIndex(index)).SampleGrad(TerrainMaterialSrg::m_detailSampler, materialContext.m_uv, materialContext.m_ddx, materialContext.m_ddy);
 }
 
 float3 GetDetailColor(in MaterialContext materialContext, in float3 macroColor)