Upgrade underscore.js

What does this MR do?

Upgrades underscore.js to 1.9 (http://underscorejs.org/#changelog). Most important part: Three years of performance improvements.

Why was this MR needed?

So underscore is up to date.

Does this MR meet the acceptance criteria?

• Review
  • Has been reviewed by Frontend
• Conform by the merge request performance guides
• Conform by the style guides
• Squashed related commits together
• Internationalization required/considered
• End-to-end tests pass (package-and-qa manual pipeline job)

What are the relevant issue numbers?

#39072 (moved)