FIX: Defer upload extension check for iOS (#15890)

accept HTML attribute is not fully supported on iOS yet and can contain
only MIME types. This changes the input to allow all files and the
extension check is performed later in JavaScript.

app/assets/javascripts/discourse/app/components/composer-editor.js

@@ -200,7 +200,10 @@ export default Component.extend(ComposerUploadUppy, {
 
   @discourseComputed()
   acceptsAllFormats() {
-    return authorizesAllExtensions(this.currentUser.staff, this.siteSettings);
+    return (
+      this.capabilities.isIOS ||
+      authorizesAllExtensions(this.currentUser.staff, this.siteSettings)
+    );
   },
 
   @discourseComputed()