Rename `assertWhenLegacyArchitectureMinifyingEnabled` to `assertLegacyArchitecture` (#50512)

Summary:
Pull Request resolved: https://github.com/facebook/react-native/pull/50512

Reland of D72389708

This renames the method to be more aligned to the fact that we're using this entrypoint both for internal
and for OSS users.

I've also added a `assertLegacyArchitectureOnlyWhenMinifyEnabled` that will run only for internal builds.

Changelog:
[Internal] [Changed] -

Reviewed By: javache

Differential Revision: D72552028

fbshipit-source-id: 2594df9ef8056f9931960117770c4b7cddd4e922