Use react-native-codegen build script in rn-tester

[janicduplessis]

Summary

Use the same script as android to build the codegen package. This also fixes the issue in #30292.

Changelog

[Internal] - Use react-native-codegen build script in rn-tester

Test Plan

Tested that using the script works when using pod install

[analysis-bot]

Platform	Engine	Arch	Size (bytes)	Diff
ios	-	universal	n/a	--

Base commit: 7dcecb2

[analysis-bot]

Platform	Engine	Arch	Size (bytes)	Diff
android	hermes	arm64-v8a	7,507,188	+0
android	hermes	armeabi-v7a	7,098,964	+0
android	hermes	x86	7,945,335	+0
android	hermes	x86_64	7,856,391	+0
android	jsc	arm64-v8a	8,971,903	+0
android	jsc	armeabi-v7a	8,546,801	+0
android	jsc	x86	8,971,534	+0
android	jsc	x86_64	9,522,859	+0

Base commit: 7dcecb2