A reaction that fails to send can now block the room's send queue, but the
timeline only surfaced failures for the item itself, its edit or its
redaction. EventTimelineItemProxy.pendingSend now also falls back to our
first failed reaction, targeting it with SendTarget.reaction(key:), so the
message shows the red exclamation mark and the sending failed alert can
retry or remove it.
In-flight reactions are deliberately ignored so reacting doesn't flash a
sending indicator on the message.
Stefan Ceriu
a87d65b05a