Support filtering saved snippets

[PIG208]

This is a possible follow-up to #863: in the bottom sheet to choose a saved snippet to insert into a message, we could add a search bar to filter the list of saved snippets.

It's not yet clear whether this is a UI feature we want; it'll depend on how the UX feels and on feedback we hear.

References

• UI design thread: #mobile-design > #F863 saved replies @ 💬
• Figma design