Browse emojis via tabs
## Problem
It is not easy nor intuitive to quickly browse through emojis by category.
## Proposal
When selecting emoji in anywhere within GitLab, view them in tabs according to the categories they are already grouped by:
| Tab | Icon |
|---------|------|
| Frequently used | `clock` |
| Smileys & People | `grinning` |
| Animals & Nature |  |
| Food & drink |  |
| Travel & places |  |
| Activity |  |
| Objects | |
| Symbols |  |
| Flags |  |
| Custom |  |
Per https://gitlab.com/groups/gitlab-org/-/epics/1820#note_209379241, these are already in `gitlab-svgs`. Disable `Custom` until we launch the ability to select a custom emoji from the list (https://gitlab.com/gitlab-org/gitlab/issues/23799).
### Behavior
- When you scroll, the tab selection updates to reflect the scroll position.
- When you select a tab, the scroll position jumps accordingly.
- Section headers are sticky as in the mockup.
**Images & Mockups:**
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### Steps
- [ ] Complete the [emoji refactoring work first](https://gitlab.com/gitlab-org/gitlab/issues/23607)
- [ ] Create separate icons for different categories (we don't want the color versions). If we can do this using existing icons and styling svgs, great.
- [ ] Consider using our [Tabs component](https://design.gitlab.com/components/tabs)
### Implementation Plan
- [ ] FE/BE to sort it out
issue