REFACTOR: handles every chat resource as an URL (#18961)

- Note this is also tweaking the UI a little bit as we are now using links/buttons in the header as needed
- It disables the find ideal channel in drawer mode, if loading `/chat` in drawer mode it will either reopen at the last position or just stay on index

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

@@ -55,7 +55,6 @@ module("Discourse Chat | Component | chat-message", function (hooks) {
       onStartSelectingMessages: () => {},
       onSelectMessage: () => {},
       bulkSelectMessages: () => {},
-      fullPage: false,
       afterReactionAdded: () => {},
       onHoverMessage: () => {},
     };
@@ -73,7 +72,6 @@ module("Discourse Chat | Component | chat-message", function (hooks) {
       onStartSelectingMessages=onStartSelectingMessages
       onSelectMessage=onSelectMessage
       bulkSelectMessages=bulkSelectMessages
-      fullPage=fullPage
       onHoverMessage=onHoverMessage
       afterReactionAdded=reStickScrollIfNeeded
     }}`;