chore(fast-html): set a={b:{c:''}} in state.json, remove x, keep a={} and x=undefined on class

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: janechu

packages/fast-html/test/fixtures/observer-map/index.html

@@ -29,7 +29,9 @@
                 Monthly: <!--fe-b$$start$$4$$metrics.engagement.monthly-4$$fe-b-->2000<!--fe-b$$end$$4$$metrics.engagement.monthly-4$$fe-b-->
             </div>
         </div>
-        <!--fe-b$$start$$5$$when-5$$fe-b--><!--fe-b$$end$$5$$when-5$$fe-b-->
+        <!--fe-b$$start$$5$$when-5$$fe-b-->
+            <span class="nested-define"><!--fe-b$$start$$0$$5-a.b.c-0$$fe-b--><!--fe-b$$end$$0$$5-a.b.c-0$$fe-b--></span>
+        <!--fe-b$$end$$5$$when-5$$fe-b-->
         <button data-fe-c-6-1>Define B</button>
         <button data-fe-c-7-1>Update C</button>
         <br>

packages/fast-html/test/fixtures/observer-map/main.ts

@@ -148,9 +148,9 @@ class ObserverMapTestElement extends FASTElement {
         activeusers: 1,
         metrics: {
             engagement: {
-                daily: 45,
-                weekly: 120,
-                monthly: 500,
+                daily: 100,
+                weekly: 500,
+                monthly: 2000,
             },
             performance: {
                 loadtime: 1.2,

packages/fast-html/test/fixtures/observer-map/state.json

@@ -18,8 +18,7 @@
             ]
         }
     ],
-    "a": null,
-    "x": null,
+    "a": { "b": { "c": "" } },
     "stats": {
         "totalusers": 2,
         "activeusers": 1,