Topic muting/unmuting/following UI redesign

This is a follow-up to #348, which aims for implementing a design matching the legacy mobile app. That doesn't support some state transitions, though.

See https://github.com/zulip/zulip-flutter/pull/1041#discussion_r1854906513 for what we might do in this direction.

Figma design: https://www.figma.com/design/1JTNtYo9memgW7vV6d0ygq/Zulip-Mobile?node-id=6329-128718&m=dev