Improve toJSON functionality and remove JSONSerializerReplacer (#4997)

CHANGELOG.md

@@ -82,9 +82,11 @@ Based on Realm JS v10.21.1: See changelog below for details on enhancements and
   ```
   * A typo was fixed in the `SubscriptionsState` enum, in which `SubscriptionsState.Superseded` now returns `superseded` in place of `Superseded`
 * `"discardLocal"` is now the default client reset mode. ([#4382](https://github.com/realm/realm-js/issues/4382))
+* Removed `Realm.JsonSerializationReplacer`. Use circular JSON serialization libraries such as [@ungap/structured-clone](https://www.npmjs.com/package/@ungap/structured-clone) and [flatted](https://www.npmjs.com/package/flatted) for stringifying Realm entities that have circular structures. The Realm entities' `toJSON` method returns plain objects and arrays (with circular references if applicable) which makes them compatible with any serialization library that supports stringifying plain JavaScript types. ([#4997](https://github.com/realm/realm-js/pull/4997))
 
 ### Enhancements
 * Small improvement to performance by caching JSI property String object [#4863](https://github.com/realm/realm-js/pull/4863)
+* Small improvement to performance for `toJSON` which should make it useful for cases where a plain representations of Realm entities are needed, e.g. when inspecting them for debugging purposes through `console.log(realmObj.toJSON())`. ([#4997](https://github.com/realm/realm-js/pull/4997)) 
 
 ### Fixed
 * None

integration-tests/tests/src/tests/dictionary.ts

@@ -64,6 +64,7 @@ describe("Dictionary", () => {
       "addListener",
       "removeListener",
       "removeAllListeners",
+      "toJSON",
     ];
     for (const name of methodNames) {
       it(`exposes a method named '${name}'`, function (this: RealmContext) {
@@ -225,6 +226,7 @@ describe("Dictionary", () => {
       // Previously this would throw on JSC, because the Dictionary was still a Proxy,
       // so modifying it tried to write to the Realm outside of a write transaction
       expect(() => {
+        // @ts-expect-error We know the field is a dict.
         jsonObject.dict.something = "test2";
       }).to.not.throw();
     });