FIX: improves unread state precision (#20615)

- Will consider a message read only one the bottom of the message has been read
- Will allow to mark a message bigger than the view port as read
- Code should be more performant as the scroll is doing less (albeit more often)
- Gives us a very precise scroll state. Problem with throttling scroll is that you could end up never getting the even where scrollTop is at 0, opening a whole range of edge cases to handle

plugins/chat/test/javascripts/components/chat-message-test.js

@@ -55,8 +55,8 @@ module("Discourse Chat | Component | chat-message", function (hooks) {
       onSelectMessage: () => {},
       bulkSelectMessages: () => {},
       onHoverMessage: () => {},
-      didShowMessage: () => {},
-      didHideMessage: () => {},
+      messageDidEnterViewport: () => {},
+      messageDidLeaveViewport: () => {},
       forceRendering: () => {},
     };
   }
@@ -74,9 +74,8 @@ module("Discourse Chat | Component | chat-message", function (hooks) {
       @onSelectMessage={{this.onSelectMessage}}
       @bulkSelectMessages={{this.bulkSelectMessages}}
       @onHoverMessage={{this.onHoverMessage}}
-      @didShowMessage={{this.didShowMessage}}
-      @didHideMessage={{this.didHideMessage}}
-      @didHideMessage={{this.didHideMessage}}
+      @messageDidEnterViewport={{this.messageDidEnterViewport}}
+      @messageDidLeaveViewport={{this.messageDidLeaveViewport}}
       @forceRendering={{this.forceRendering}}
     />
   `;