Test failed locally in `TestPublicChannelMention`. This test seems to
specify that the same message may arrive twice with the same ID, so
rather than overthinking this one I propose we just use `FirstOrDefault`.
```csharp
TearDown : System.AggregateException : One or more errors occurred.
(Sequence contains more than one matching element)
----> System.InvalidOperationException : Sequence contains more than
one matching element
--TearDown
at System.Threading.Tasks.Task.ThrowIfExceptional(Boolean
includeTaskCanceledExceptions)
at System.Threading.Tasks.Task.Wait(Int32 millisecondsTimeout,
CancellationToken cancellationToken)
at osu.Framework.Extensions.TaskExtensions.WaitSafely(Task task)
at osu.Framework.Testing.TestScene.checkForErrors()
--InvalidOperationException
at System.Linq.ThrowHelper.ThrowMoreThanOneMatchException()
at System.Linq.Enumerable.TryGetSingle[TSource](IEnumerable`1 source,
Func`2 predicate, Boolean& found)
at System.Linq.Enumerable.SingleOrDefault[TSource](IEnumerable`1
source, Func`2 predicate)
at
osu.Game.Overlays.Chat.DrawableChannel.<processMessageHighlighting>b__14_0()
in
/Users/dean/Projects/osu/osu.Game/Overlays/Chat/DrawableChannel.cs:line
102
at osu.Framework.Threading.ScheduledDelegate.RunTaskInternal()
```
Without this change, there would be a couple of pixels between each list
item where nothing would be hovered. This is a pretty annoying UX which
we should be avoiding we possible.
Also removes the necessity of scheduling as it actually never worked as
intended, `Scheduler` will still update even when the chat line is
masked away, and the animation will never be held anyways.
The new duration of the animation should be enough for long scrolls
either way.
In the case a message arrives and the chat overlay is hidden, clicking
on the mention notification will not work as the `HighlightedMessage`
bindable callback will execute before the scheduled `newMessagesArrived`
logic (which was hanging since the message arrived until the chat
overlay became open because of the notification).
Simplify things by always scheduling the `HighlightedMessage` bindable
callback.
Adds components `ChannelListing` and `ChannelListing` item with visual
test. Essentially a more simplified version of the existing
`ChannelSelectionOverlay` component.
Correctly implements `IFilterable` behaviour to filter child channel
items. Channel joined state is based on the underlying `Joined` bindable
of the `Channel` class.
Channel join/leave events are exposed via `OnRequestJoin` and
`OnRequestLeave` events which should be handled by parent component.
Requires a cached `OverlayColourScheme` instance to be provided by the
parent overlay component when added.
`currentChannel` gets instantiated once the chat overlay is open, while
`HighlightMessage` could be called while the chat overlay has never been
open.
This will all be rewritten with the new chat overlay design anyways, so
should be fine for now.
