Left align emoji picker on descriptions and notes

What does this MR do and why?

Move emoji picker to the right of the trigger button (left-aligned with it).

Also some related refactoring split from !115972 (merged)

1. Remove unused addButtonClass class
2. Add 'boundary' prop to award list to allow containing it within a modal (for tasks)

Screenshots or screen recordings

before	after

The emoji picker at the top right of notes remains unachanged:

How to set up and validate locally

1. Add reaction to issue/Incident/Epic/MR description or notes

MR acceptance checklist

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