Add docs to support content resizing on iOS

[LouiseHsu]

This pr adds some docs to support dynamic content resizing for add to app scenarios.

https://github.com/flutter/flutter/pull/177410

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[gemini-code-assist[bot]]

Summary of Changes

Hello @LouiseHsu, I'm Gemini Code Assist[^1]! 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 enhances the iOS 'add-to-app' documentation by providing comprehensive guidance on implementing dynamic content resizing for embedded Flutter views. It outlines the necessary steps to enable this feature, details the limitations concerning certain Flutter widgets, and offers practical code examples and a sample project to assist developers in integrating Flutter content that can adapt its size dynamically within an iOS application.

Highlights

• New Documentation Section: A new section titled 'Content Sized Views' has been added to the iOS 'add-to-app' documentation.
• Enabling Content Resizing: The documentation now includes instructions and code examples (in Swift and Objective-C) on how to enable isAutoResizable for FlutterViewController to allow embedded Flutter views to size themselves based on their content.
• Restrictions and Unsupported Widgets: Detailed information has been added regarding the restrictions of content-sized Flutter views, specifically highlighting that widgets with unbounded size (e.g., ListView) and those that defer to children for sizing (e.g., LayoutBuilder) are not supported.
• Widget Compatibility Testing: A Dart code example using UnconstrainedBox is provided to help developers test the usability of various Flutter widgets within a content-sized view context.
• Sample Project Reference: A link to a sample project demonstrating content resizing for iOS 'add-to-app' scenarios has been included for practical reference.

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[flutter-website-bot]

Visit the preview URL for this PR (updated for commit 774ac1d5b13c4c6a41235a869c90a873a2b9d6fa):

https://flutter-docs-prod--pr12810-content-resizing-ha8g1duf.web.app