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`.
