Consolidate hermes-executor-debug and -release inside a single target (#35454)

Summary:
Pull Request resolved: https://github.com/facebook/react-native/pull/35454

Historically, we used to have hermes-executor debug and release as separate dynamic libraries.
This makes it impossible to prefab this library, so I have to reconcile it into a single library.

This will also help keep the setup consistent with the internal (BUCK) where we have a single target.

Changelog:
[Internal] [Changed] - Consolidate hermes-executor-debug and -release inside a single target

Reviewed By: cipolleschi

Differential Revision: D41519119

fbshipit-source-id: d9ddc30b72164daa29c735836ea433fd4d917fc8