[GH-23555] Do not block global backspace key press for contenteditable's (#23626)

* [GH-23555] Backspace is forbidden globally

* [GH-23555] Backspace is forbidden globally (refactoring)

---------

Co-authored-by: Andrey Karavashkin <akaravashkin@stsoft.ru>

webapp/channels/src/components/logged_in/logged_in.tsx

@@ -15,8 +15,8 @@ import WebSocketClient from 'client/web_websocket_client.jsx';
 import BrowserStore from 'stores/browser_store';
 import {UserProfile} from '@mattermost/types/users';
 import {Channel} from '@mattermost/types/channels';
-
-const BACKSPACE_CHAR = 8;
+import {isKeyPressed} from 'utils/keyboard';
+import Constants from 'utils/constants';
 
 declare global {
     interface Window {
@@ -205,8 +205,20 @@ export default class LoggedIn extends React.PureComponent<Props> {
 
     private handleBackSpace = (e: KeyboardEvent): void => {
         const excludedElements = ['input', 'textarea'];
+        const targetElement = e.target as HTMLElement;
 
-        if (e.which === BACKSPACE_CHAR && !(excludedElements.includes((e.target as HTMLElement).tagName.toLowerCase()))) {
+        if (!targetElement) {
+            return;
+        }
+
+        const targetsTagName = targetElement.tagName.toLowerCase();
+        const isTargetNotContentEditable = targetElement.getAttribute?.('contenteditable') !== 'true';
+
+        if (
+            isKeyPressed(e, Constants.KeyCodes.BACKSPACE) &&
+            !(excludedElements.includes(targetsTagName)) &&
+            isTargetNotContentEditable
+        ) {
             e.preventDefault();
         }
     };