Resolve "Web IDE MR/branch dropdown closes unexpectedly"

What does this MR do?

Fixes Issue #61332 (closed) Web IDE MR/branch dropdown closes unexpectedly

Now, when you click outside the input box in the Web IDE MR or branch dropdown, it will focus on the search input instead. This is done to be consistent with the behaviour of the select2 dropdown component. An example of that component can be seen on the New Project page (project URL dropdown)

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry for user-facing changes, or community contribution. Check the link for other scenarios.
• [NA] Documentation created/updated or follow-up review issue created
• Code review guidelines
• Merge request performance guidelines
• Style guides
• [NA] Database guides
• [NA] 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. Closes #61332 (closed)