Provides initial implementation of new chat overlay in component
`ChatOverlayV2`. Contains only the basic functionality required for
a functioning chat overlay according to the new design with the intent
of added the rest of the functionality in subsequent PRs.
Backports existing tests for the current chat overlay except for ones
testing keyboard shortcuts (since they haven't been added) and tab
closing behaviour (since no tabs).
Reference design: https://www.figma.com/file/f8b2dHp9LJCMOqYP4mdrPZ/Client%2FChat?node-id=1%3A297
Adds new component `ChannelList` which makes up the sidebar channel
selector of the new chat design. Contains two separate fill flows for
public and private `ChannelItem` child components.
Exposed bindable `SelectorActive` to indicate current state of the "Add
more channels" button. Requires `Bindable<Channel>` from parent
component.
Renames and updates the `TestSceneChannelListItem` to
`TestSceneChannelList` to make use of new component and having both
tests seemed redundant.
Reference design: https://www.figma.com/file/f8b2dHp9LJCMOqYP4mdrPZ/Client%2FChat?node-id=1%3A297
Adds new component `ChatTextBox`.
Exposes `BindableBool` `ShowSearch` to change text input behaviour
between normal and search behaviour.
Adds new component `ChatTextBar`.
Exposes `BindableBool` `ShowSearch` which toggles between showing current
chat channel or search icon.
Additionally binds to child `ChatTextBox` components.
Requires a cached `Bindable<Channel>` instance to be managed by a parent
component.
Adds new component `ChannelControlItem` and it's child components to be
used as the clickable control in the new chat sidebar for joined
channels.
Has public properties `HasUnread` and `MentionCount` to control the
display of the channel having unread messages or mentions of the user.
Channel select/join requests are exposed via `OnRequestSelect` and
`OnRequestLeave` events respectively which should be handled by a parent
component.
Requires a cached `Bindable<Channel>` instance to be managed by a parent
component.
Requires a cached `OveralayColourScheme` instance to be provided by a
parent component.
