Formatted all app/assets/javascripts to underscore naming convention

What does this MR do?

Changes all javascript file names to user underscores as delimiter.

This will be enforced in the docs in a different MR !6782 (closed).

Are there points in the code the reviewer needs to double check?

Why was this MR needed?

Consistency.

Screenshots (if relevant)

Does this MR meet the acceptance criteria?

• CHANGELOG entry added
• Documentation created/updated
• API support added
• Tests
  • Added for this feature/bug
  • All builds are passing
• Conform by the merge request performance guides
• Conform by the style guides
• Branch has no merge conflicts with master (if it does - rebase it please)
• Squashed related commits together

What are the relevant issue numbers?

Closes #23118 (closed)