gpui_linux: Clear X11 urgency hint on focus

[melocene]

Objective

Fixes #61679

Solution

Clear the X11 WM_HINTS urgency flag when a window receives focus, while preserving the other window manager hints.

Testing

• Did you test these changes? If so, how?

  • cargo check -p gpui_linux
  • cargo test -p gpui_linux --lib
  • Manual Xfce verification was not completed as the dev version would not properly authenticate me with GitHub Copilot, though it did show as signed in.

Reviewers can reproduce #61679 on XFCE using xprop WM_HINTS to confirm that the urgency hint is cleared after focusing Zed.

• Are there any parts that need more testing?

Shouldn't be as this is just another method in a similar style as the existing.

• How can other people (reviewers) test your changes? Is there anything specific they need to know?

Compile and run Zed on a system running XFCE4.

• If relevant, what platforms did you test these changes on, and are there any important ones you can't test?

Arch Linux with XFCE 4.20

Self-Review Checklist:

• I've reviewed my own diff for quality, security, and reliability
• Unsafe blocks (if any) have justifying comments
• [] The content adheres to Zed's UI standards (UX/UI and icon guidelines)
• Tests cover the new/changed behavior
• Performance impact has been considered and is acceptable

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Release Notes:

• Fixed Zed continuing to demand attention after regaining focus on X11.