[native] implement emoji keyboard button on reaction selection popover

Summary:
implemented the emoji keyboard button on the reaction selection popover. The button uses a plus icon, and when the user presses on it, the emoji keyboard opens, showing all the emojis the user can use to react

Figma

Depends on D6454
Linear Task: ENG-2777

Test Plan:
Please watch the demo video to see the changes I made:

Reviewers: atul, tomek

Reviewed By: tomek

Subscribers: ashoat, tomek, atul

Differential Revision: https://phab.comm.dev/D6455