1. Sticker pack toolbar is now at the bottom of the "sticker keyboard" in chat.
2. Sticker pack toolbar is now "floating" in a a glass panel on iOS 26, both in sticker keyboard in chat and in full-screen sticker picker in media editor.
3. There's some helper text when "recent stickers" panel is empty.
This included:
- Removing unavailable inits wholesale if no longer `required`
- Marking a few classes `final` so they could continue using
`Self(...)` rather than `OWSWhatever(...)`
