fix: fix @react-native-community/cli-platform-apple not being resolved correctly (microsoft#2820)

## Summary:

`@react-native-community/cli-platform-apple` is not correctly resolved
in pnpm setups:

```
% DEBUG=react-native yarn build:macos
/~/packages/app/example/node_modules/react-native-macos/react-native.config.js: @react-native-community/cli-platform-apple not found, the react-native.config.js may be unusable.
info Bundling macos...
error Invalid platform "macos" selected.
info Available platforms are: "android", "ios", "windows". If you are trying to bundle for an out-of-tree platform, it may not be installed.
```

## Test Plan:

n/a

Author: tido64

packages/react-native/react-native.config.js

@@ -71,8 +71,14 @@ try {
 // [macOS
 let apple;
 try {
+  const iosPath = require.resolve('@react-native-community/cli-platform-ios', {
+    paths: [process.cwd()],
+  });
   // $FlowFixMe[untyped-import]
-  apple = require('@react-native-community/cli-platform-apple');
+  apple = findCommunityPlatformPackage(
+    '@react-native-community/cli-platform-apple',
+    iosPath,
+  );
 } catch {
   if (verbose) {
     console.warn(
@@ -156,7 +162,7 @@ if (android != null) {
 
 // [macOS
 config.commands.push(...macosCommands);
-if (apple != null) {
+if (apple) {
   config.platforms.macos = {
     linkConfig: () => {
       return {