Mark as unread

[SpiritCroc]

WIP: https://github.com/SchildiChat/matrix-react-sdk/commits/mark-as-unread

Mandatory

• Try out New feature: marking rooms as unread [MSC2867] matrix-org/matrix-react-sdk#6314
• Enable by default
• Render with green exclamation mark as in Android
• Do not show if already unread
• Fix room detail view saying "Something went wrong!" when the mentions panel is open
• Muted rooms should be allowed to render as "marked as unread" in the same way as unmuted rooms
• Move strings to Schildi-specific strings, and add missing ones
  • Move original strings: SchildiChat/matrix-react-sdk@0692440
  • Add "Mark as read" string from SchildiChat/matrix-react-sdk@d6ec5c4
• Change icon for "Mark as unread" action

Nice to have

• Add "mark as read" action to show instead of "mark as unread" when the chat is already unread
  • which also updates the read receipt (and thus also marks chats as read that had new messages)
• After using the "mark as (un)read" actions, the chat entry is still rendered in some kind of selected state, which makes it harder to see if it actually worked. Can we remove that selected state automatically?
• Show home if current room is marked unread
• Use UnstableValue class from matrix-js-sdk?
• Once merged, enable by default on Android