Editor: Keep excerpt popover below media modal

[MicahelE]

Summary

When the Excerpt panel is open, opening the Media Library can leave the Excerpt popover above the Media Library. This can cover part of the modal and make it difficult to use.

This change moves the Excerpt popover below the Media Library only while the modal is open. The normal popover behavior is unchanged after the modal closes.

Screenshots

Before:

After:

Testing

• Opened a new post in the block editor.
• Opened the Excerpt panel.
• Opened the Media Library with Set featured image.
• Confirmed the Media Library covers the Excerpt popover.
• Closed the Media Library and confirmed the Excerpt popover returns to its normal position.
• Ran npm run grunt -- precommit:css.

Trac ticket: https://core.trac.wordpress.org/ticket/66031

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Props micahele.

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[MicahelE]

Screenshots

Before:

After: