Syncs the vue test utils helpers

What does this MR do?

This MR uses the javascript export * from 'file' pattern to allow us to use the Vue test utils helpers from our Jest specs in Karma. Previously we were copy/pasting the entire file which made keeping things up to date a bit of a chore.

With this handy-dandy pattern, it's a chore no more!

Any time we add a new function to spec/frontend/helpers/vue_test_utils_helper.js, it gets automatically added to spec/javascripts/helpers/vue_test_utils_helper.js. Then, once we move off of karma completely, we can delete the karma version of this file and we're clean again.

Does this MR meet the acceptance criteria?

Conformity

• [-] Changelog entry for user-facing changes, or community contribution. Check the link for other scenarios.
• [-] 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