Extract member specializations from name (#56076)

Summary:
Pull Request resolved: https://github.com/facebook/react-native/pull/56076

Changelog: [Internal]

Updates the C++ API snapshot generator to extract specializations from name when a member is created, instead of relying on the one stored in the name string.

It also makes out-of-class definitions of members to be skipped in the snapshot as those were essentially duplicated between their declaration inside the class, and the initialization outside of it.

Reviewed By: cipolleschi

Differential Revision: D96303740

fbshipit-source-id: d649cb04bd7370af55ce707d607a372d7b4115b4