Make the value field of a TrackedValue general from the first instance

packages/@glimmer/validator/lib/tracked-value.ts

@@ -29,6 +29,19 @@ export class TrackedValue<Value = unknown> implements Reactive<Value> {
   readonly #tag: UpdatableTag;
 
   constructor(value: Value, options: ReactiveOptions<Value>) {
+    /**
+     * If we let V8 try to completely optimize TrackedValue for
+     *   for each type of `value`,
+     *     that performs worse than making V8 only use one internal
+     *     internal version of the class for each type of `value`.
+     *
+     * The first value of another kind makes V8 throw away
+     *   the optimized code that reads the field.
+     *
+     * The field starts as `undefined`,
+     *   so a number here makes it general from the first instance.
+     */
+    this.#value = 0 as Value;
     this.#value = value;
     this.#options = options;
     this.#tag = createUpdatableTag();