AF-2920: add Dart 2 compatible snippets

[sebastianmalysa-wf]

Description

Several changes and additions to the over_react component boiler plate were required to reach parity between the current over_react transformer and the new Dart 2 over_react builder. This PR adds snippets that are compatible with the Dart 2 over_react builder.

Test

• open VS code, navigate to preferences and select User Snippets
• select New Global Snippet file..., name the file and paste in contents of snippets.json
• you should now be able to invoke the snippets in any file with a .dart extension by calling the snippet prefix

Review

@evanweible-wf @corwinsheahan-wf @JaceHensley

[JaceHensley]

@sebastianmalysa-wf happy to merge this and release it and if you or someone else wants it over there I'd be happy to transfer ownership of this repo and extension