Merge all core codegen into FBReactNativeSpec

[javache]

Summary:

rncore, FBReactNativeSpec and FBReactNativeComponentSpec contain the same symbols, which leads to conflicts when we try to merge them into a single shared library. Cleanup the duplication and standardize on FBReactNativeSpec everywhere. I've left the Android OSS targets names as is, to avoid breaking deps.

This aligns react-native's package.json with the codegen tooling supported across iOS and Android, which is a single target for all all type-derived codegen.

Changelog: [Internal]

Differential Revision: D55037569

[facebook-github-bot]

This pull request was exported from Phabricator. Differential Revision: D55037569

[facebook-github-bot]

This pull request was exported from Phabricator. Differential Revision: D55037569

[facebook-github-bot]

This pull request was exported from Phabricator. Differential Revision: D55037569

[facebook-github-bot]

This pull request was exported from Phabricator. Differential Revision: D55037569

[facebook-github-bot]

This pull request was exported from Phabricator. Differential Revision: D55037569

[facebook-github-bot]

This pull request was exported from Phabricator. Differential Revision: D55037569

[facebook-github-bot]

This pull request was exported from Phabricator. Differential Revision: D55037569

[facebook-github-bot]

This pull request was exported from Phabricator. Differential Revision: D55037569

[facebook-github-bot]

This pull request was exported from Phabricator. Differential Revision: D55037569

[facebook-github-bot]

This pull request has been merged in facebook/react-native@95ed8a6123024afd03227358ab4b165fdf87b270.

[react-native-bot]

This pull request was successfully merged by @javache in 95ed8a6123024afd03227358ab4b165fdf87b270

^{When will my fix make it into a release? | How to file a pick request?}