Refactor PageLayout.Pane resizable API: separate onWidthChange and currentWidth props

[Copilot]

Refactors PageLayout.Pane resizable configuration to use separate onWidthChange callback and currentWidth props, and simplifies resizable to a boolean.

Before:

<PageLayout.Pane
  resizable={{
    width: currentWidth,
    persist: (width) => setCurrentWidth(width)
  }}
/>

After:

<PageLayout.Pane
  resizable
  currentWidth={currentWidth}
  onWidthChange={setCurrentWidth}
/>

Changelog

New

• PageLayout.Pane: currentWidth?: number prop for controlled width
• PageLayout.Pane: onWidthChange?: (width: number) => void callback for width changes

Changed

• resizable prop simplified to: boolean | undefined (no longer accepts configuration objects)
• When onWidthChange is provided, it takes precedence over localStorage persistence

Removed

• resizable.width property (replaced by currentWidth prop)
• PersistConfig type and configuration object pattern {persist: false | 'localStorage' | fn}
• PersistFunction and SaveOptions types
• isPersistConfig, isCustomPersistFunction, and isResizableEnabled helper functions

Rollout strategy

• Patch release
• Minor release
• Major release; if selected, include a written rollout or migration plan
• None; if selected, include a brief description as to why

Rationale: Adds new props and simplifies the API. Maintains backward compatibility for resizable={true} but removes the configuration object pattern in favor of the simpler onWidthChange prop for custom persistence.

Testing & Reviewing

• Stories updated to demonstrate controlled component pattern with currentWidth + onWidthChange
• Test coverage includes onWidthChange precedence over localStorage
• Verify resizable panes work with and without onWidthChange
• 54 unit tests passing (22 tests removed related to deprecated configuration objects)

Merge checklist

• Added/updated tests
• Added/updated documentation
• Added/updated previews (Storybook)
• Changes are SSR compatible
• Tested in Chrome
• Tested in Firefox
• Tested in Safari
• Tested in Edge
• (GitHub staff only) Integration tests pass at github/github (Learn more about how to run integration tests)

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Latest commit: 1ffd338

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[github-actions]

👋 Hi, this pull request contains changes to the source code that github/github-ui depends on. If you are GitHub staff, test these changes with github/github-ui using the integration workflow. Or, apply the integration-tests: skipped manually label to skip these checks.

[mattcosta7]

@copilot we should remove these options now for resizable, which is only a boolean or undefind now

[Copilot]

Simplified resizable to just boolean | undefined in commit 1ffd338.

Removed:

• PersistConfig, PersistFunction, SaveOptions types
• isPersistConfig, isCustomPersistFunction, isResizableEnabled helpers
• 22 tests related to persist config options

The API is now simpler:

• resizable={true} - Enable resizing with localStorage (if no onWidthChange)
• resizable={false} or omit - Disable resizing
• Use onWidthChange prop for custom persistence instead of {persist: fn}