Notification Comment Details: show new Comment details view

[ScoutHarris]

When the details of a Comment notification is shown, display the content using the new Comment details view.

• Add feature flag.
  • Notifications > Comment Details: show new details view for cached comment #17850
• Fetch Comment object from Core Data.
  • Notifications > Comment Details: show new details view for cached comment #17850
• Fetch Comment object from API.
  • Notifications > Comment Details: fetch comment if it is not cached #17890
  • Comments: add REST endpoint to fetch a single comment WordPressKit-iOS#486
• Display Comment.
  • Notifications > Comment Details: show previous and next arrows in nav bar #17897
  • Notifications > Comment Details: show previous/next comments #17923
    • Disable arrow buttons if there is no previous/next notification.
    • Handle when arrow buttons are tapped within the Comments filter.
  • Handle when arrow buttons are tapped in the All or Unread filters (i.e. show NotificationDetailsViewController when notification type changes and vice versa).
    • Notifications: show new Comment detail from previous/next buttons #17954
    • Notifications > Comments: show Notification detail from previous/next buttons #17959
  • Set the nav bar titles for Notifications.
    • Notifications > Comment Details: show new details view for cached comment #17850
  • Show NRV
    • Notification Comments: add wrapper view controller to display details #18049
    • Notification Comment details: show loading and error views #18062
    • Notification Comment details: remove gap at the top #18064
    • Notification Comment details: set background color to fix transition oddity #18082
    • Notification Comment Details: hide back button title in threaded comments #18131
  • Comment Notifications: mark as read when viewed with previous/next buttons #17980
  • Notifications > Comment details header: fix misc issues #17969
  • Notifications > Comment details: fix reply headers #17973
  • Notifications > Comments: fix notification selection issues #17978
  • Notifications > Comments: remove Notification when Comment is removed #17992
  • Notifications split view: set selected Notification after removing moderated #18002
  • Notifications split view: immediately remove deleted comment notifications #18010
  • Notifications: remove notification for deleted Comment #18028
• Verify accessibility.
• Notification Comment details: add tracks for actions #18070
• Fix comment details for a site the user doesn’t have a role on.
  • Notification Comment Details: get comment from post if blog is unavailable #18129
  • Notification Comment Details: post comment functionality #18130
• Notification Comment Details: enable feature for release #18141