[iOS] Build codegen package while using old architecture

[Saadnajmi]

Summary

Fixes #36097

When building RNTester with the old architecture, we skip a call to build_codegen, which will build the JS package at packages/react-native-codegen. This is needed for the Xcode Script phase Generate Specs. This causes a build with fabric disabled to fail. We can fix this by ensuring we call build_codegen in both paper and fabric.

We've had this change in React Native macOS already since 0.68: microsoft@1175372

Changelog

[IOS] [FIXED] - Build codegen package while using old architecture

Test Plan

CI should suffice. Locally built RN-Tester without fabric with and without my change to show that disabling fabric will only succeed with this change included.
While running pod install, you should now see this extra line with the old architecture:

[Codegen] building ./../../packages/react-native-codegen.

[analysis-bot]

Platform	Engine	Arch	Size (bytes)	Diff
android	hermes	arm64-v8a	8,475,500	+0
android	hermes	armeabi-v7a	7,796,979	+0
android	hermes	x86	8,951,538	+0
android	hermes	x86_64	8,809,339	+0
android	jsc	arm64-v8a	9,113,287	+0
android	jsc	armeabi-v7a	8,309,960	+0
android	jsc	x86	9,164,875	+0
android	jsc	x86_64	9,423,765	+0

Base commit: 9eaf6f5
Branch: main

[facebook-github-bot]

@cipolleschi has imported this pull request. If you are a Meta employee, you can view this diff on Phabricator.

[facebook-github-bot]

@cipolleschi merged this pull request in 90327d9.