It should let you just use your phone keyboard to enter the emoji the same way you would when typing a post
Discussion
Logic would dictate, but I can only do that within a post. When I long press the heart beneath a post to "react" to it, I get what you see in the screenshot. The bottom list of emojis are animated, which is not what I want. 
New reaction symbol.
(It'll bring up your keyboard)
Enter the emoji you want.
Save.