Summary:
Apple will require XCode 15 next year to ship to the app store, and it aligns with how we build and test React Native internally.

XCode 15 and 14.3 add support for a lot of [missing C++ 20 features](https://developer.apple.com/xcode/cpp/#c++20) from earlier versions as well.

Last I was aware, Riccardo was onboard with bumping min supported in 0.74 to XCode 15. This change does a slightly more conservative bump to min 14.3, and main of 15.0 (though we might want to move these before 0.74 comes out).

All of this will get migrated over to GHA soon enough as well, but... formalizing this is the only thing blocking usage of C++ 20 ranges today.

Changelog:
[ios][breaking] - Require XCode >= 14.3

Pull Request resolved: https://github.com/facebook/react-native/pull/41798

Test Plan:
1. CircleCI Passes
2. Can still boot RNTester from XCode with code signing related changes.

Reviewed By: cortinico

Differential Revision: D51840617

Pulled By: NickGerleman

fbshipit-source-id: 58f8951a436eb7c892a00432a8aad0ddd0a49da1