[Flyouts] Support for "large" child flyout

[tsullivan]

Summary

This PR adds support for size="fill" for EuiFlyoutChild.

Fill mode for for EuiFlyout will come as a later PR.

Why are we making this change?

Part of https://github.com/elastic/kibana-team/issues/1844

Screenshots

Main=s, Child=fill, type=overlay

Main=s, Child=fill, type=push

Impact to users

QA

Remove or strikethrough items that do not apply to your PR.

General checklist

• Browser QA
  • Checked in both light and dark modes
  • Checked in both MacOS and Windows high contrast modes
    • (emulate forced colors if you do not have access to a Windows machine.)
  • Checked in mobile
  • Checked in Chrome, Safari, Edge, and Firefox
  • Checked for accessibility including keyboard-only and screenreader modes
• Docs site QA
  • Added documentation
  • Props have proper autodocs (using @default if default values are missing) and playground toggles
  • Checked Code Sandbox works for any docs examples
• Code quality checklist
  • Added or updated jest and cypress tests
  • Updated visual regression tests
• Release checklist
  • A changelog entry exists and is marked appropriately.
  • If applicable, added the breaking change issue label (and filled out the breaking change checklist)
• Designer checklist
  • If applicable, file an issue to update EUI's Figma library with any corresponding UI changes. (This is an internal repo, if you are external to Elastic, ask a maintainer to submit this request)

[tsullivan]

This is consistent with the behavior of the existing code: for push type main flyouts, the child flyout only occupies the amount of space it should have if the main flyout width changes to match it. But, this behavior becomes more problematic for the scenario where the child flyout has size="fill". If the main flyout has type="push", then then underlying content is squeezed into the remaining space. When the screen gets smaller in that scenario and the child flyout is stacked above the main flyout, the underlying content is squeezed into 10vw of space.

[tsullivan]

I completely refactored this story to better take advantage of args. Now we don't need separate stories to demo different configurations of props.

[elasticmachine]

💚 Build Succeeded

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• Commit: b723a1f
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History

• 💚 Build #931 succeeded e6b2830
• 💚 Build #930 succeeded f10cae0

[elasticmachine]

💚 Build Succeeded

• Buildkite Build
• Commit: b723a1f

History

• 💚 Build #4496 succeeded e6b2830
• 💚 Build #4495 succeeded f10cae0

[tsullivan]

Replaced with #8982