Fixing reverted !41014

What does this MR do?

Provides the full contents of !41014 (merged) plus the fix that led to failed tests and the reverse of the original MR. To make things easier to control, the only difference between this MR and the original one:

Index: app/assets/javascripts/snippets/index.js
IDEA additional info:
Subsystem: com.intellij.openapi.diff.impl.patch.CharsetEP
<+>UTF-8
===================================================================
--- app/assets/javascripts/snippets/index.js	(revision ea1a3b0901d5a5baadc4ccff90f1ba778122f06d)
+++ app/assets/javascripts/snippets/index.js	(revision 5ed56f4d600761471ead64de38e72768caf95218)
@@ -19,7 +19,7 @@
     defaultClient: createDefaultClient(),
   });
 
-  const { visibilityLevels, selectedLevel, multipleLevelsRestricted, ...restDataset } = el.dataset;
+  const { visibilityLevels = '[]', selectedLevel, multipleLevelsRestricted, ...restDataset } = el.dataset;
 
   apolloProvider.clients.defaultClient.cache.writeData({
     data: {

Screenshots

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• Separation of EE specific content

Availability and Testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• Tested in all supported browsers
• Informed Infrastructure department of a default or new setting change, if applicable per definition of done

Security

If this MR contains changes to processing or storing of credentials or tokens, authorization and authentication methods and other items described in the security review guidelines:

• Label as security and @ mention @gitlab-com/gl-security/appsec
• The MR includes necessary changes to maintain consistency between UI, API, email, or other methods
• Security reports checked/validated by a reviewer from the AppSec team

References #241468 (closed)