Probe Cache: Fixed conversion shader to use the proper mip when input texture was not the right size.

ScriptableRenderPipeline/Core/Resources/BlitCubeTextureFace.shader

             SAMPLERCUBE(sampler_InputTex);
 
             float _FaceIndex;
+            float _LoD;
 
             struct Attributes
             {
 
             float4 frag (Varyings input) : SV_Target
             {
-                return SAMPLE_TEXTURECUBE(_InputTex, sampler_InputTex, input.texcoord);
+                return SAMPLE_TEXTURECUBE_LOD(_InputTex, sampler_InputTex, input.texcoord, _LoD);
             }
 
             ENDHLSL

ScriptableRenderPipeline/HDRenderPipeline/Lighting/ReflectionProbeCache.cs

 {
     public class ReflectionProbeCache
     {
+        internal static readonly int s_InputTexID = Shader.PropertyToID("_InputTex");
+        internal static readonly int s_LoDID = Shader.PropertyToID("_LoD");
+        internal static readonly int s_FaceIndexID = Shader.PropertyToID("_FaceIndex");
+
         enum ProbeFilteringState
         {
             Convolving,
         // We can't use Graphics.ConvertTexture here because it does not work with a RenderTexture as destination.
         void ConvertTexture(CommandBuffer cmd, Texture input, RenderTexture target)
         {
-            m_ConvertTextureMPB.SetTexture("_InputTex", input);
+            m_ConvertTextureMPB.SetTexture(s_InputTexID, input);
+            m_ConvertTextureMPB.SetFloat(s_LoDID, 0.0f); // We want to convert mip 0 to whatever the size of the destination cache is.
-                m_ConvertTextureMPB.SetFloat("_FaceIndex", (float)f);
+                m_ConvertTextureMPB.SetFloat(s_FaceIndexID, (float)f);
                 CoreUtils.SetRenderTarget(cmd, target, ClearFlag.None, Color.black, 0, (CubemapFace)f);
                 CoreUtils.DrawFullScreen(cmd, m_ConvertTextureMaterial, m_ConvertTextureMPB);
             }