Replace _uid reference with uniqueId

What does this MR do?

See !55283 (comment 521153936)

This MR replaces a reference to a private Vue property _uid. Thankfully it's rather straightforward to just use lodash's uniqueId here 🎉

Does this MR meet the acceptance criteria?

Conformity

• [ ] Does this MR need a changelog? No user facing change
• Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• Separation of EE specific content