Replace deprecated String.prototype.substr() (#17949)

* Replace deprecated String.prototype.substr()

.substr() is deprecated so we replace it with .slice() which works similarily but isn't deprecated

* Change String.prototype.substring() to String.prototype.slice()

.substring() and .slice() work very similary but .slice() is a bit faster and stricter

* Add ESLint rule to forbid usage of .substr and .substring

.substr() is deprecated and .substring() is very similar to .slice() so better to use .slice() at all times

Signed-off-by: Tobias Speicher <rootcommander@gmail.com>

app/javascript/mastodon/features/status/components/card.js

@@ -32,7 +32,7 @@ const trim = (text, len) => {
     return text;
   }
 
-  return text.substring(0, cut) + (text.length > len ? '…' : '');
+  return text.slice(0, cut) + (text.length > len ? '…' : '');
 };
 
 const domParser = new DOMParser();