Fix Material Validator enum getting stuck in Rendering Debugger when enabling another mode

Fix https://jira.unity3d.com/browse/UUM-70780

HDRP Rendering Debugger UI maps multiple different enum dropdowns into a single internal enum, and therefore these modes are mutually exclusive. The mechanism to do this relies on enumIndices that get reset. In this case the enumindex reset was missing, causing the enum dropdown UI drawer to get stuck in the previous value even though the internal enum value had changed.

Author: arttu-peltonen

Packages/com.unity.render-pipelines.high-definition/Runtime/Debug/DebugDisplay.cs

@@ -431,6 +431,7 @@ internal void ResetExclusiveEnumIndices()
                 gBufferEnumIndex = 0;
                 lightingFulscreenDebugModeEnumIndex = 0;
                 renderingFulscreenDebugModeEnumIndex = 0;
+                materialValidatorDebugModeEnumIndex = 0;
                 renderingHistoryBuffersViewEnumIndex = -1;
             }
         }