DEV: various improvements to devex on chat (#21612)

- Improves styleguide support
- Adds toggle color scheme to styleguide
- Adds properties mutators to styleguide
- Attempts to quit a session as soon as done with it in system specs, this should at least free resources faster
- Refactors fabricators to simplify them
- Adds more fabricators (uploads for example)
- Starts implementing components pattern in system specs
- Uses Chat::Message creator to create messages in system specs, this should help to have more real specs as the side effects should now happen

plugins/chat/assets/javascripts/discourse/components/chat-composer.hbs

@@ -9,7 +9,6 @@
         this.currentMessage
         this.currentMessage.inReplyTo
       }}
-      @icon={{if this.currentMessage.editing "pencil-alt" "reply"}}
       @cancelAction={{this.onCancel}}
     />
   {{/if}}
@@ -26,7 +25,7 @@
     }}
     {{did-update this.didUpdateMessage this.currentMessage}}
     {{did-update this.didUpdateInReplyTo this.currentMessage.inReplyTo}}
-    {{did-insert this.setupAppEvents}}
+    {{did-insert this.setup}}
     {{will-destroy this.teardown}}
     {{will-destroy this.cancelPersistDraft}}
   >
@@ -71,7 +70,7 @@
           {{on "click" this.onSend}}
           @icon="paper-plane"
           class="chat-composer__send-btn"
-          title="chat.composer.send"
+          title={{i18n "chat.composer.send"}}
           disabled={{or this.disabled (not this.sendEnabled)}}
           tabindex={{if this.sendEnabled 0 -1}}
           {{on "focus" (fn this.computeIsFocused true)}}