Migration docs improvements (#13034)

Author: jerelmiller

docs/source/migrating/apollo-client-4-migration.mdx

@@ -366,6 +366,12 @@ End: Inserted by Apollo Client 3->4 migration codemod.
 
 ### Running the codemod
 
+<Note>
+
+The codemod requires a Node.js version that supports loading ECMAScript modules with `require`. See the table in the [Node.js documentation](https://nodejs.org/api/modules.html#loading-ecmascript-modules-using-require) for the versions that support this feature (you might need to expand the "History" section to see the table.)
+
+</Note>
+
 To run the codemod, use the following command:
 
 ```sh showLineNumbers=false
@@ -378,6 +384,12 @@ This command behaves similarly to [`jscodeshift`](https://github.com/facebook/js
 
 </Note>
 
+<Note>
+
+This example targets the `src` directory with the codemod. Replace `src` with the file pattern applicable to your file structure if it differs.
+
+</Note>
+
 For more details on the available options, run the command using the `--help` option.
 
 ```sh showLineNumbers=false
@@ -393,12 +405,6 @@ npx @apollo/client-codemod-migrate-3-to-4 --parser ts --extensions ts src
 npx @apollo/client-codemod-migrate-3-to-4 --parser tsx --extensions tsx src
 ```
 
-<Note>
-
-This example targets the `src` directory with the codemod. Replace `src` with the file pattern applicable to your file structure if it differs.
-
-</Note>
-
 ### Running specific modifications
 
 If you prefer to migrate your application more selectively instead of all at once, you can specify specific modifications using the `--codemod` option. For example, to run only the `imports` and `links` modifications, run the following command:
@@ -1032,6 +1038,60 @@ If you rely on the initial value to read data from the subscription, we recommen
 
 </Caution>
 
+### `ObservableQuery` no longer inherits from `Observable`
+
+`ObservableQuery` instances returned from `client.watchQuery` no longer inherit from `Observable`. This might cause TypeScript errors when using `ObservableQuery` with some RxJS utilities that expect `Observable` instances, such as [`firstValueFrom`](https://rxjs.dev/api/index/function/firstValueFrom).
+
+Convert `ObservableQuery` to an `Observable` using the [`from`](https://rxjs.dev/api/index/function/from) function.
+
+```ts
+import { from } from "rxjs";
+
+const observable = from(observableQuery);
+//    ^? Observable<ObservableQuery.Result<MaybeMasked<TData>>>
+```
+
+<Note>
+
+`ObservableQuery` implements the [`Subscribable`](https://rxjs.dev/api/index/interface/Subscribable) interface, so you can call `subscribe` directly without converting to an `Observable`. It also implements the `pipe` function, so you can chain operators.<br/><br/>
+
+Use `from` only for functions that require an `Observable` instance.
+
+</Note>
+
+### Removal of `Observable` utilities
+
+Apollo Client 3 included several utilities for working with `Observable` instances from the `zen-observable` library. Apollo Client 4 removes these utilities in favor of RxJS's operators.
+
+#### `fromError`
+
+Use the [`throwError`](https://rxjs.dev/api/index/function/throwError) function instead.
+
+```ts
+const observable = fromError(new Error("Oops"));// [!code --]
+const observable = throwError(() => {// [!code ++:3]
+  return new Error("Oops");
+});
+```
+
+#### `fromPromise`
+
+Use the [`from`](https://rxjs.dev/api/index/function/from) function instead.
+
+```ts
+const observable = fromPromise(promise);// [!code --]
+const observable = from(promise);// [!code ++]
+```
+
+#### `toPromise`
+
+Use the [`firstValueFrom`](https://rxjs.dev/api/index/function/firstValueFrom) function instead.
+
+```ts
+const promise = toPromise(observable);// [!code --]
+const promise = firstValueFrom(observable);// [!code ++]
+```
+
 ## New error handling
 
 Error handling in Apollo Client 4 has changed significantly to be more predictable and intuitive.