[VFX] Close VFX template window on domain reload

Jira: UUM-62433

Steps to reproduce:
- Start new project, import VFX graph
- Right click -> create new VFX graph to open Template window
- Without closing in, cause a domain reload (hit play, switch editor theme)
=> Observe window becomes empty

 💡Proposed solution: closing window would be the best option here

Author: julienamsellem

Packages/com.unity.visualeffectgraph/Editor/TemplateWindow/VFXTemplateWindow.cs

@@ -156,6 +156,21 @@ private void LoadTemplates()
             m_ListOfTemplates.ExpandAll();
         }
 
+        private void OnEnable()
+        {
+            AssemblyReloadEvents.beforeAssemblyReload += OnBeforeAssemblyReload;
+        }
+
+        private void OnDisable()
+        {
+            AssemblyReloadEvents.beforeAssemblyReload -= OnBeforeAssemblyReload;
+        }
+
+        private void OnBeforeAssemblyReload()
+        {
+            this.Close();
+        }
+
         private void OnDestroy()
         {
             EditorPrefs.SetString(LastSelectedGuidKey, m_LastSelectedTemplateGuid);