Add "quick reaction" buttons to the top of the emoji picker

In other apps like Element and Zulip, they give you a short list of commonly-used emojis in an easy-to-reach location. You can also search through the full list, but they pre-select a few that they know lots of people will want.

We should do that too, with a simple horizontal row of emojis at the top of our picker. These should include:

• Heart
• Smile
• Thumbs Up
• Tada
• Whatever others we chose on Android