[0.87] Bootstrap Metro from InitializeCore until setup-env is graph-reachable

Summary:
Fresh 0.87 projects redbox on launch with:

  Failed to call into JavaScript module method RCTDeviceEventEmitter.emit().
  Module has not been registered as callable.
  Registered callable JavaScript modules (n = 1): AppRegistry.

Core initialization never runs. Metro's `getModulesRunBeforeMainModule`
(see metro/src/lib/getAppendScripts.js) only emits the run-before `__r()`
call for a module that is *already present in the bundle graph*, and
silently skips it otherwise.

to `src/setup-env.js`. `InitializeCore` is reachable in the graph (imported
by `Libraries/ReactPrivate/ReactNativePrivateInitializeCore.js`), but
`src/setup-env.js` is imported by nothing, so Metro skips it and core init
never runs. The two modules are functionally identical (both call
`setUpDefaultReactNativeEnvironment().default()`).

Evidence (bundle tail):
- setup-env target:     `__r(0);`            (broken)
- InitializeCore target: `__r(110); __r(0);`  (fixed)

This is an INTERIM stopgap to unblock the 0.87 RC. It only changes the
internal Metro bootstrap target back to `InitializeCore`; the public
`react-native/setup-env` entry point and its deprecation of InitializeCore
are unchanged. The proper fix (make `setup-env` graph-reachable, or make
Metro treat `getModulesRunBeforeMainModule` entries as graph roots) should
land on main and supersede this.

Changelog:
[General][Fixed] - Fix apps failing to boot ("RCTDeviceEventEmitter not
registered as callable") due to core init not running.

Test Plan:
- `yarn test-release-local -t RNTestProject -p iOS`: app boots without redbox.
- Bundle tail now contains `__r(<InitializeCore>); __r(0);` instead of just `__r(0);`.

Author: zeyap

packages/community-cli-plugin/src/utils/loadMetroConfig.js

@@ -58,15 +58,15 @@ function getCommunityCliDefaultConfig(
   return {
     resolver,
     serializer: {
-      // We can include multiple copies of setup-env here because Metro will
+      // We can include multiple copies of InitializeCore here because metro will
       // only add ones that are already part of the bundle
       getModulesRunBeforeMainModule: () => [
-        require.resolve('react-native/setup-env', {
+        require.resolve('react-native/Libraries/Core/InitializeCore', {
           paths: [ctx.root],
         }),
         ...outOfTreePlatforms.map(platform =>
           require.resolve(
-            `${ctx.platforms[platform].npmPackageName}/setup-env`,
+            `${ctx.platforms[platform].npmPackageName}/Libraries/Core/InitializeCore`,
             {paths: [ctx.root]},
           ),
         ),

packages/metro-config/src/index.flow.js

@@ -61,7 +61,7 @@ export function getDefaultConfig(projectRoot: string): ConfigT {
     serializer: {
       // NOTE: Overridden in community-cli-plugin
       getModulesRunBeforeMainModule: () => [
-        require.resolve('react-native/setup-env'),
+        require.resolve('react-native/Libraries/Core/InitializeCore'),
       ],
       getPolyfills: () => require('@react-native/js-polyfills')(),
       isThirdPartyModule({path: modulePath}: Readonly<{path: string, ...}>) {