FIX: Ensure hashtag autocomplete is not behind keyboard in chat (#19419)

We must set `treatAsTextarea` to true when using autocomplete
in the chat composer, since it is at the bottom of the screen
we always want to show it above the composer. This fixes the
issue where the hashtag autocomplete results went behind the
keyboard on mobile (which was not happening for mentions).

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

@@ -410,9 +410,12 @@ export default Component.extend(TextareaTextManipulation, {
       this.site.hashtag_configurations["chat-composer"],
       $textarea,
       this.siteSettings,
-      (value) => {
-        this.set("value", value);
-        return this._focusTextArea();
+      {
+        treatAsTextarea: true,
+        afterComplete: (value) => {
+          this.set("value", value);
+          return this._focusTextArea();
+        },
       }
     );
   },