Everything: Rich text redux (#5625)

* lord save me

* UI/ChatBox: Use the new `defStyle` param for `RenderMarkup`

The previous iteration didn't work because `AddMessage` can't inherit
its color from the PushColor (since we're not doing actual tag stacks
anymore).

* rebase touchup

Content.Client/Examine/ExamineSystem.cs

@@ -181,9 +181,9 @@ namespace Content.Client.Examine
                 message = response.Message;
             }
 
-            foreach (var msg in message.Tags.OfType<FormattedMessage.TagText>())
+            foreach (var msg in message.Sections)
             {
-                if (string.IsNullOrWhiteSpace(msg.Text)) continue;
+                if (string.IsNullOrWhiteSpace(msg.Content)) continue;
 
                 var richLabel = new RichTextLabel();
                 richLabel.SetMessage(message);