Update template to xcode 12

[janicduplessis]

Summary

This makes a few change to the template xcodeproj

• Update to recommended settings for Xcode 12
• Remove the main.jsbundle file that doesn't exists, this file is included automatically in the app bundle and doesn't need to be in xcode (it won't even be at that path).
• Add -e to the bundle images script. It seems like Xcode doesn't fail the build on script errors anymore so this makes it so the build stop. If it doesn't stop the app will launch and crash because the bundle doesn't exist (note this is only if running the app in release mode since in debug we don't generate the bundle).

Changelog

[iOS] [Added] - Update template to xcode 12

Test Plan

Made the same changes in an app and made sure it ran well.

[analysis-bot]

Platform	Engine	Arch	Size (bytes)	Diff
android	hermes	arm64-v8a	7,385,801	0
android	hermes	armeabi-v7a	7,013,117	0
android	hermes	x86	7,828,013	0
android	hermes	x86_64	7,717,499	0
android	jsc	arm64-v8a	9,532,102	0
android	jsc	armeabi-v7a	9,147,130	-4,096
android	jsc	x86	9,396,778	0
android	jsc	x86_64	9,978,488	0

Base commit: 0d02c60

[analysis-bot]

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

Base commit: 0d02c60

[facebook-github-bot]

@sammy-SC has imported this pull request. If you are a Facebook employee, you can view this diff on Phabricator.

[react-native-bot]

This pull request was successfully merged by @janicduplessis in 6685aba.

^{When will my fix make it into a release? | Upcoming Releases}

[anujraghuvanshi]

I've XCode 11.5.

I am trying to run react native project with version 0.64.1. Should it run? Or XCode 12 is min requirement now if want to run with the latest react native version? Not getting any clue from anywhere so asking this here. Kindly confirm.