[Flyout System] Remove isOpen prop

[tkajtoch]

Summary

Resolves #9065

This PR removes the recently added isOpen prop due to incompatibility with some of the flyout system features. The complexity of fixing the incompatibility ended up being more involving than just removing the supplementary prop I had previously decided would be worth having. We can still add the isOpen prop in the future if we decide it's worth it, but it's not related to the Flyout System project and can be safely omitted at this time.

Why are we making this change?

This work is part of the Flyout System project.

Impact to users

isOpen prop removal has no impact on users since it existed only temporarily in a feature branch.

QA

Regular flyouts

• Open EuiFlyout -> Playground story and confirm that clicking the Toggle flyout button toggles the visibility of the flyout
  Note: Due to the removal of the isOpen prop, there's no closing animation. That's expected

Managed flyouts - playground

• Open EuiFlyout -> Flyout Manager -> Playground
• Click Open Main Flyout and confirm the flyout opens
• Click Open child panel and confirm the child flyout opens to the left
• Click Close Main Flyout and confirm that both flyouts close at the same time

Managed flyouts - Multi-session example

• Open EuiFlyout -> Flyout Manager -> Multi-session example
• Click Open Session A and confirm the flyout opens
• Click Open child flyout
• Click Open Session B and confirm the Session A - Main and Session A - Child flyouts disappear and Session B - Main shows up
• Click Back and confirm it transitions to session A with Session A - Main and Session A - Child flyouts being visible

General checklist

• Browser QA
  • Checked in both light and dark modes
  • Checked for accessibility including keyboard-only and screenreader modes
• Code quality checklist
  • Added or updated jest and cypress tests

[elasticmachine]

💚 Build Succeeded

• Buildkite Build
• Commit: a9cbb70
• Documentation website
• Storybook

History

• 💔 Build #1452 failed e7124df

cc @tkajtoch

[elasticmachine]

💚 Build Succeeded

• Buildkite Build
• Commit: a9cbb70

History

• 💔 Build #4861 failed e7124df

cc @tkajtoch

[tsullivan]

LGTM! I love how this simplifies the implementation, results in better performance, and will keep animations consistent for all flyouts.