Action sheet for a DM conversation

[chrisbobbe]

We have a topic action sheet that's reached by long-pressing any of these:

• A topic row in the Inbox
• A recipient header in the message list
• An area in the message-list app bar
• (Will be offered on the Channels page, with Show topics on channels page #412)

This issue is for a similar action sheet for DM conversations. It should offer:

• (for group DMs): a button that opens a page showing the users in the conversation; see Figma design for this page
• Mark conversation as read

It could also offer:

• (for non-self 1:1 DMs): a button to mute/unmute the user (requires Mute muted users #296)

It should be reachable by long-pressing any of these:

• A DM row in the Inbox
• A recipient header in the message list
• The area of the message-list app bar that identifies the narrow
• The "Direct messages" (recent DMs) page

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It looks like we don't have this action sheet in zulip-mobile. The visual design should match the existing topic action sheet.

[Abhisheksainii]

picking this up