Update messageListItem onLongPress colors

issue: https://gitlab.e.foundation/e/backlog/-/issues/4723

- remove checked icon showing on message selected state
- update background color of message on-selected stage to color_default_gray1 for light-mode & color_default_gray2 for dark-mode for better visibility
- update messageList preview text color to secondary text color for better visibility
- update messageList item on-active background color to accent color
- change message threadCount background box color to secondary text color for better visibility