Add search functionality

[cpaleop]

Is your feature request related to a problem? Please describe.
I guess the problem a user can face is complexity. A search functionality would reduce the mental-load of user going through each one of the emojis to find which one they want.

Describe the solution you'd like
A search field can be added on the top of the bottom-sheet-dialog, prompting the user to search for an emoji. The search functionality could query the name of the CategoryUnicodes.

While the user types in the search field the emojis that match the query would show under their respective category.

Describe alternatives you've considered
None

Additional context
Attaching a screenshot from Slack's search functionality, I believe the layout is outdated though.