Migrate related items tree specs to Jest & VTU

What does this MR do?

This MR migrates some Karma specs to Jest & Vue Test Utils. Affected specs have the following criteria:

• They test some tooltip-related behavior
• They reside in the ee/spec/javascripts/related_items_tree/components/ directory

We migrate those specs to lay the groundwork for upgrading bootstrap-vue because BootstrapVue's tooltip component has been heavily refactored, causing several failures in our test suites. By migrating these specs to Jest & VTU, we'll be able to focus on a single approach for making our specs compatible with the new tooltip component.

Does this MR meet the acceptance criteria?

Conformity

• [-] Changelog entry
• [-] 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

Availability 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