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.Server/Headset/HeadsetComponent.cs

@@ -86,7 +86,7 @@ namespace Content.Server.Headset
             RadioRequested = false;
         }
 
-        public void Examine(FormattedMessage message, bool inDetailsRange)
+        public void Examine(FormattedMessage.Builder message, bool inDetailsRange)
         {
             message.AddText(Loc.GetString("examine-radio-frequency", ("frequency", BroadcastFrequency)));
             message.AddText("\n");