[SPIKE] Use extra native package and do a Toast

[hypest]

Spike to try out a way to add an extra native module accessible via RN but only added on the gb-mobile and WPAndroid side.

No Gutenberg repo side PR needed.

Check out the toast loaded when the editor starts, which is done during "setup". Here's is the code and here's a video:

https://user-images.githubusercontent.com/1032913/135291028-9730667b-4eb3-4cf1-9bd4-8df4935f79bf.mp4

To test:

PR submission checklist:

• [ ] I have considered adding unit tests where possible.
• [ ] I have considered if this change warrants user-facing release notes more info and have added them to RELEASE-NOTES.txt if necessary.