Summary:
Make the script ready for picking in 0.62.0-rc.3.
* Rename the script to remove ambiguity. “autolinking” is a CLI feature where 3rd-party pods are automatically discovered: https://github.com/react-native-community/cli/blob/master/docs/autolinking.md
* Make the Flipper version of the pods configurable, as requested [here](https://github.com/facebook/react-native/pull/28044#discussion_r378662636).
* Make RNTester’s Podfile use the same form as the template–including enabling Flipper by moving the CPP define into the right place in the Xcode project and out of the Podfile.
* Get rid of Podfile.lock thrashing by making the default CDN spec source explicit.
## Changelog
[iOS] [Changed] - Disambiguate autolinking-ios.rb script from CLI’s “autolinking” feature and bring RNTester & template in line.
Pull Request resolved: https://github.com/facebook/react-native/pull/28077
Test Plan: RNTester builds, as does a new application.
Reviewed By: PeteTheHeat
Differential Revision: D19956392
Pulled By: TheSavior
fbshipit-source-id: 6c800ddb646b49fc45c088978e2794cd7b60ea48
4118d79826