FIX: Broken error reporting in modals (and other places) (#23680)

1. actually call `popupAjaxError`, thanks :P
2. don't close a modal on error
3. use `extractError()` instead of manually joining error messages
4. …or passing just the error object to `this.flash`

plugins/chat/assets/javascripts/discourse/components/chat/modal/create-channel.js

@@ -9,6 +9,7 @@ import { inject as service } from "@ember/service";
 import { isBlank, isPresent } from "@ember/utils";
 import { htmlSafe } from "@ember/template";
 import { tracked } from "@glimmer/tracking";
+import { extractError } from "discourse/lib/ajax-error";
 
 const DEFAULT_HINT = htmlSafe(
   I18n.t("chat.create_channel.choose_category.default_hint", {
@@ -108,17 +109,16 @@ export default class ChatModalCreateChannel extends Component {
     }
   }
 
-  #createChannel(data) {
-    return this.chatApi
-      .createChannel(data)
-      .then((channel) => {
-        this.args.closeModal();
-        this.chatChannelsManager.follow(channel);
-        this.router.transitionTo("chat.channel", ...channel.routeModels);
-      })
-      .catch((e) => {
-        this.flash = e.jqXHR.responseJSON.errors[0];
-      });
+  async #createChannel(data) {
+    try {
+      const channel = await this.chatApi.createChannel(data);
+
+      this.args.closeModal();
+      this.chatChannelsManager.follow(channel);
+      this.router.transitionTo("chat.channel", ...channel.routeModels);
+    } catch (e) {
+      this.flash = extractError(e);
+    }
   }
 
   #buildCategorySlug(category) {

plugins/chat/assets/javascripts/discourse/components/chat/modal/edit-channel-description.js

@@ -2,6 +2,7 @@ import Component from "@glimmer/component";
 import { action } from "@ember/object";
 import { tracked } from "@glimmer/tracking";
 import { inject as service } from "@ember/service";
+import { extractError } from "discourse/lib/ajax-error";
 
 const DESCRIPTION_MAX_LENGTH = 280;
 
@@ -27,18 +28,16 @@ export default class ChatModalEditChannelDescription extends Component {
   }
 
   @action
-  onSaveChatChannelDescription() {
-    return this.chatApi
-      .updateChannel(this.channel.id, { description: this.editedDescription })
-      .then((result) => {
-        this.channel.description = result.channel.description;
-        this.args.closeModal();
-      })
-      .catch((event) => {
-        if (event.jqXHR?.responseJSON?.errors) {
-          this.flash = event.jqXHR.responseJSON.errors.join("\n");
-        }
+  async onSaveChatChannelDescription() {
+    try {
+      const result = await this.chatApi.updateChannel(this.channel.id, {
+        description: this.editedDescription,
       });
+      this.channel.description = result.channel.description;
+      this.args.closeModal();
+    } catch (error) {
+      this.flash = extractError(error);
+    }
   }
 
   @action