Adds cacheExtent and cacheExtentStyle migration guide

[chunhtai]

migration guide for flutter/flutter#181092

Presubmit checklist

• If you are unwilling, or unable, to sign the CLA, even for a tiny, one-word PR, please file an issue instead of a PR.
• If this PR is not meant to land until a future stable release, mark it as draft with an explanation.
• This PR follows the Google Developer Documentation Style Guidelines—for example, it doesn't use i.e. or e.g., and it avoids I and we (first-person pronouns).
• This PR uses semantic line breaks
  of 80 characters or fewer.

[gemini-code-assist]

Summary of Changes

Hello @chunhtai, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request focuses on enhancing the documentation for a significant breaking change within Flutter's scrolling mechanism. It provides a comprehensive migration guide for developers transitioning from the deprecated cacheExtent and cacheExtentStyle properties to the new scrollCacheExtent property. The guide details how to update both widget and RenderObject layer implementations, ensuring a smoother upgrade path and promoting the use of a more explicit and type-safe API for scroll caching.

Highlights

• New Migration Guide Added: This pull request introduces a new migration guide document for the deprecation of cacheExtent and cacheExtentStyle properties in Flutter's scrolling widgets.
• Replacement Property: The deprecated properties are replaced by a new scrollCacheExtent property, which utilizes a ScrollCacheExtent object to encapsulate both the value and the caching strategy (pixels or viewport).
• Improved Clarity and Type Safety: The change aims to provide clearer intent and better type safety by explicitly defining the caching strategy within the ScrollCacheExtent object, moving away from the previous ambiguous interpretation of a double value.

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Changelog

• src/content/release/breaking-changes/index.md
  • Added a new entry and link for the 'Deprecated cacheExtent and cacheExtentStyle' migration guide.
• src/content/release/breaking-changes/scroll-cache-extent.md
  • New file created, containing the detailed migration guide for the cacheExtent and cacheExtentStyle deprecation.
  • Includes sections on summary, background, migration steps for widget and RenderObject layers, timeline, and references to API documentation and the original PR.

Activity

• The pull request adds a new documentation page to guide users through a breaking change related to scroll caching.
• It links to the original pull request (Introduce ScrollCacheExtent and also fixes unbound shrinkwrap cache ex… flutter#181092) where the ScrollCacheExtent was introduced.
• The PR description includes a standard presubmit checklist, indicating adherence to documentation style guidelines and semantic line breaks.

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[gemini-code-assist]

Code Review

This pull request adds a migration guide for the deprecation of cacheExtent and cacheExtentStyle. The guide is well-structured and provides clear before-and-after code examples. My review includes suggestions to adhere to the project's documentation style guide, specifically regarding semantic line breaks, and to enhance the completeness of the migration examples for the RenderObject layer.

[flutter-website-bot]

Visit the preview URL for this PR (updated for commit f8171d0):

https://flutter-docs-prod--pr13044-scrollcacheextent-c4yk928m.web.app

[sfshaza2]

lgtm