Fix IDE file dropdown

What does this MR do?

• Fixes IDE file dropdown by using mouseleave event instead of mouseout (which was being triggered for leaving children inside the parent).
• Refactors the new_dropdown/index component to receive isOpen as a prop, instead of managing it as a data prop. Why? This seemed like a good opportunity to reduce some of the complexity by collocating the isOpen state with the component that has the information to change it.

Screenshots

Before	After

Does this MR meet the acceptance criteria?

Conformity

• [-] Changelog entry Not needed because this regression was introduced and fixed in the same release.
• [-] Documentation created/updated or follow-up review issue created
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• Separation of EE specific content

Performance 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

Closes #60021 (closed)