Implement month separator for the Gallery.

Improve day separator rendering in the timeline.
Use Today, Yesterday, and the name of the day if less than 7 days and do not render the year for the current year.
Improve date format for the media viewer.
Rework how date and time are computed.
ActionListView: Time can take more space, so update the layout.

libraries/mediaviewer/test/src/main/kotlin/io/element/android/libraries/mediaviewer/test/FakeLocalMediaFactory.kt

@@ -40,7 +40,8 @@ class FakeLocalMediaFactory(
             senderId = null,
             senderName = null,
             senderAvatar = null,
-            dateSent = null
+            dateSent = null,
+            dateSentFull = null,
         )
         return aLocalMedia(uri, mediaInfo)
     }