Components: add unit test __experimentalExpandOnFocus unit tests for FormTokenField

[chad1008]

What?

Adds three new unit tests to FormTokenField for the __experimentalExpandOnFocus prop

Why?

Ensure the suggestion list expands (or not) appropriately depending on the value of this prop, and that it doesn't reopen when the component is blurred. See #57002

How?

The first two tests check that the suggestions respond properly to the logic updated in the above PR. This ensures that

1. when __experimentalExpandOnFocus is true, selecting a visible suggestion will not close the suggestion list, because the component still has focus.
2. When it's false, the suggestion list does close upon a selection, because focus alone is not enough to cause it to expand

A third test then confirms that clicking outside the bounds of the component does not cause the suggestion list to reopen, which was the specific regression addressed in the above PR.

Testing Instructions

Confirm the new tests pass

[github-actions]

Flaky tests detected in 333952b.
Some tests passed with failed attempts. The failures may not be related to this commit but are still reported for visibility. See the documentation for more information.

🔍 Workflow run URL: https://github.com/WordPress/gutenberg/actions/runs/7226853842
📝 Reported issues:

• [Flaky Test] should display the "Manage Fonts" icon #56776 in /test/e2e/specs/site-editor/font-library.spec.js

[ciampo]

Thank you for working on it!

Tested by undoing the changes in #57002, and verifying that the last test fails

[talldan]

Thanks for adding the test! 😄