FIX: simplify body scroll lock on iOS (#30696)

This will have the following advantages:
- removes a very annoying bug which was making text selection super hard on iOS
- removes the flashing of header when transitioning from disable to enable body scroll lock

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

@@ -12,10 +12,6 @@ import { Promise } from "rsvp";
 import EmojiPickerDetached from "discourse/components/emoji-picker/detached";
 import InsertHyperlink from "discourse/components/modal/insert-hyperlink";
 import { SKIP } from "discourse/lib/autocomplete";
-import {
-  disableBodyScroll,
-  enableBodyScroll,
-} from "discourse/lib/body-scroll-lock";
 import { setupHashtagAutocomplete } from "discourse/lib/hashtag-autocomplete";
 import { emojiUrlFor } from "discourse/lib/text";
 import userSearch from "discourse/lib/user-search";
@@ -285,22 +281,20 @@ export default class ChatComposer extends Component {
   }
 
   @action
-  onTextareaFocusOut(event) {
+  onTextareaFocusOut() {
     this.isFocused = false;
-    enableBodyScroll(event.target);
   }
 
   @action
   onTextareaFocusIn(event) {
     this.isFocused = true;
-    const textarea = event.target;
-    disableBodyScroll(textarea);
 
     if (!this.capabilities.isIOS) {
       return;
     }
 
     // hack to prevent the whole viewport to move on focus input
+    const textarea = event.target;
     textarea.style.transform = "translateY(-99999px)";
     textarea.focus();
     window.requestAnimationFrame(() => {

plugins/chat/assets/stylesheets/common/chat-channel.scss

@@ -22,5 +22,7 @@
     color: var(--primary-medium);
     font-size: var(--font-down-1);
     padding: 0.5em 0.25em 0.25em;
+    touch-action: none;
+    height: 100%;
   }
 }