Add an emoji picker to the annotation editor

[mkdir-washington-edu]

The problem
Users request the ability to add emojis to their notes to allow them to more easily show engagement, approval, etc.

The solution
From Jared:

I think we could utilize a library like Emoji Mart, it allows you to enable a picker which is highly customizable and easy to implement. They also provide a type-ahead option called "headless search" which we could customize to allow users to select the emoji which matched their search. The type-ahead option is a little less straightforward, but manageable.

Here's what it might look like in the annotation editor: https://www.figma.com/design/aml5dQS86CLBnUkT3JRgFE/Hypothesis---Emoji-Picker?node-id=0-1&p=f&t=1PSfLTwpF4FSsC2m-0