Refactors `ChatLine` component to use more sensible override properties
and layout using grid container. Moves creation of username component
into its own method to simplify BDL.
Updates padding of base `DrawableChannel` flow padding.
Removes usage of `ChatOverlayDrawableChannel` since it's overrides are
no longer needed.
Updates usage of `StandAloneChatDisplay` to use new override properties
of `DrawableChannel`.
Moves `DaySeparator` chat component to it's own file and update it to
match new chat design. Makes use of several virtual attributes that can
be overridden to update spacing and layout in other usage contexts.
Remove redundant usage of `ChatOverlayDaySeparator`, since the new
design is now part of the base class.
Create `StandAloneDaySeparator` to use in `StandAloneChatDisplay` which
overrides attributes to match correct spacing and layout for its design.
Ensure that `DrawableChannel.CreateDaySeparator` returns type of
`DaySeparator` instead of `Drawable`.
Add dummy channel `DummySelectorChannel` which should be set as the
current channel in the channel manager when the selector in the chat
overlay should be shown.
Refactors the `ChannelListItem` to not show mention pill and close
button when the channel is the dummy selector channel.
Ensure that the `ChannelList` selects the dummy channel on clicking the
selector item.
Removes `ChannelListSelector` as it is no longer needed.
Removes the `setCurrent` parameter from `ChannelManager.JoinChannel`
method as it is no longer needed.
Updates the `DaySeparator` component to have separately settable colours
for the text and the lines.
Updates existing overrides of the `DaySeparator` to use the new colour
setter.
Create new `ChatOverlayDrawableChannel` with adjusted spacing and new
`DaySeparator` colours.
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).
