Pinned message improvements

[mahibi]

• Improve scolling in pinned message container

• Text and icons change according to dark/light
  - vertical padding matches the input field (likely 16dp) for the container
  - padding in the container seems to be too large as well, should also be 16dp
  - furthermore I wouldn't use a fab, but rather have a 3-dot menu in the container at the top right/end

• ref Dark mode issues with message pinning #5717

i will merge it and further bugs can be solved with follow ups.

• issue with authors (for a follow up PR):

1. pin as user 1
2. in the same conversation, pin an other message as user 2

bug: message 2 is shown, but user1 is shown as author

• ref Message Pinning 📌 #5535 (comment)

For further polishing we might want to to make the menu headline bold else it currenrly looks like a menu item without an icon followed by a divider but the time info is not clickable. Else I think it could also be an option to put the time into the pinned message field also.

• ref internal

Thanks. I'm on v23 RC1. Setting custom dismissal time for pinned messages doesn't work. Once time is selected, tapping Ok does nothing.