The `TimelinePanel` uses two timers to coordinate read marker and read receipt
updates. When the read receipt timer fires, we advance the receipt and send the
latest state of both your receipt and marker to the server. When the read marker
timer fires, we advance the marker visually, but do not send anything to the
server: we were relying on the slightly different schedule of the read receipt
to actually send the updated read marker. This means there's a time window where
it's possible to visually advance the read marker without ever sending it to the
server (if you change rooms before the receipt timer fires again).
To simplify the behaviour here and ensure we always commit the updated marker
when we move it, this change sends an update to the server at the same time as
moving the marker.
It's possible this may improve some of the behaviour reported in
https://github.com/vector-im/riot-web/issues/12338.
It had ~32px of overflow causing a horizontal scrollbar. Turns out the layout engine gets confused when hidden elements are at the end of a flexbox, so we just move them higher in the DOM (where they logically still make sense).
The remaining changes are all alignment and misc changes in that respect, and probably not obvious.
The tag options are not implemented out of concern for diff size.
This splits the context menu classes out to a new "iconized" style which is common across a number of context menus, including the UserMenu.
Some of the badge/sublist styles had to change to better accommodate the menu icon lining up.
This also contains the framework required for https://github.com/vector-im/riot-web/issues/13961
The 'sort by' radio buttons are blocked by https://github.com/matrix-org/matrix-react-sdk/pull/4731 as it contains the styles needed.
The 'unread rooms' checkbox is intentionally not hooked up. This is a more complicated refactoring that needs to be done.
The message preview checkbox works, though the previews remain hardcoded in this change. The primary intent of this change is to have a good enough context menu and the hover states.
The hover states are as described in the design.
