Add priority to material extensions

src/materials/MaterialExtender.ts

             }
 
         material.materialExtensions = [...material.materialExtensions || [], ...exts]
+            .sort((a, b)=>(b.priority || 0) - (a.priority || 0))
 
         if (!(material as any).__ext_beforeRenderListen) {
             (material as any).__ext_beforeRenderListen = true

src/materials/MaterialExtension.ts

      */
     getUiConfig?: (material: IMaterial, refreshUi: UiObjectConfig['uiRefresh']) => UiObjectConfig | undefined
 
+    /**
+     * Higher priority extensions are applied first.
+     */
+    priority?: number // default 0
+
     updateVersion?: number
     // eslint-disable-next-line @typescript-eslint/naming-convention
     __setDirty?: () => void // set by MaterialExtender, this increments updateVersion, which ends up calling needsUpdate on all the materials with this extension