Previously we were hiding the entire app bar on mobile phones in landscape orientation. However now that the app bar supports a small 'subtitle' element, we should show only the subtitle in this case to match the designs.
The subtitle still hides on tap, just like the footer.
On mobile, the ringing status indicator is supposed to display in the header rather than on a tile. The exact layout differs between Android and iOS. To get it right I had to refactor AppBar to use CSS grid templates.
(Also, I changed my mind about the exact ringing data I needed out of CallViewModel - sorry. A little move of the ringtone audio renderer into its own component was necessary to accommodate that.)
It was rather confusing that matrixLivekitMembers$ gives you objects of type RemoteMatrixLivekitMembers and yet the *local* member would often be among these. I've attempted to clear this up. To my knowledge this wasn't creating any bugs.
The rule of thumb to avoid resource leaks is that you should never call ObservableScope methods in a callback unless the ObservableScope is directly passed to or created inside that callback. I had a go at codifying this as a lint rule.
I noticed that calls to createDisplayNameBehavior$ and createAvatarUrlBehavior$ were technically leaking resources since they reused the ObservableScope from their outer scope, which in practice lasts for the entire lifetime of the CallViewModel. This would not have had any noticeable effect unless you had other participants leave and rejoin the same call many thousands of times.
I found our code's internal model of ringing a little overgrown (it had superfluous states like 'unknown') and difficult to extend with metadata or callbacks relating to ring attempts. By modeling ringing instead as a stream of ring attempts, where each attempt has an intent, a recipient, and an eventual outcome (accept/decline/timeout), I find it more natural to work with.
This makes room for a future 'try again' callback to allow ringing someone again after a timeout, and also forced me to look for a simpler solution to the duplicate leave sound effects. I exposed the intent of the ringing attempt to the call UI so I can later use it in the header.
