Show channel/topic at top of channel/topic action sheet

[gnprice]

When the user opens the channel action sheet or topic action sheet (e.g. by long-pressing on the channel or topic name somewhere), the resulting bottom sheet should show at the top the name of the channel, or the channel and topic, respectively.

References

• Chat thread: #mobile > abbreviated headings @ 💬
• Figma design: I believe there is one. (The first step for this issue would be to find it and post the link here.)
• Similar issue (but more complex to implement): Show message text in bottom sheet #217