Update documentation for iOS 27, macOS 27, and Xcode 27 support

[MuthuGCodes]

Description of what this PR is changing or adding, and why:

Updates documentation across docs.flutter.dev to support iOS 27, macOS 27 ("Golden Gate"), and Xcode 27:

• Supported platforms (sites/docs/src/content/reference/supported-platforms.md):
  • Update iOS supported version range to 15 to 27.
  • Update macOS supported version range to Monterey (12) to Golden Gate (27).
• UIScene migration guide (sites/docs/src/content/release/breaking-changes/uiscenedelegate.md):
  • Add a version note documenting that Xcode 27 (iOS 27 SDK) mandates UIScene and unmigrated UIKit apps fail to launch on startup.
  • Update the timeline section to reflect enforcement in Xcode 27.
• macOS building (sites/docs/src/content/platform-integration/macos/building.md):
  • Add an informational warning note regarding the ongoing deprecation of macOS Intel (x64) hardware, linking to the deprecation strategy.
• iOS setup (sites/docs/src/content/platform-integration/ios/setup.md):
  • Provide launch commands for both Xcode 27+ (open -a DeviceHub) and Xcode 26 (open -a Simulator).
  • Refine simulator recommendation phrasing per style guide and remove unused [Flutter on latest iOS] link definition.
• Retire outdated iOS latest tracker (sites/docs/src/content/platform-integration/ios/ios-latest.md):
  • Remove outdated feature tracking page.
  • Remove corresponding entry from sidenav (default.yml) and landing card (platform-integration/index.md).
• Hosting redirects (sites/docs/firebase.json):
  • Add 301 redirect from /release/breaking-changes/uiscene-lifecycle-ios to /release/breaking-changes/uiscenedelegate (resolves 404 from Flutter 3.47 release blog).
  • Add 301 redirect from /platform-integration/ios/ios-latest to /platform-integration/ios (gracefully handling existing references including past release notes).

Issues fixed by this PR (if any):
b/540919760

PRs or commits this PR depends on (if any):
None

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.

[flutter-website-bot]

Staged preview of the updated docs.flutter.dev site (updated for commit 1f322b3):

https://flutter-docs-prod--docs-pr13872-ios-27-flutter-updates-1cbocxcw.web.app

[flutter-website-bot]

Staged preview of the updated flutter.dev site (updated for commit 1f322b3):

https://flutter-dev-230821--www-pr13872-ios-27-flutter-updates-kv8qww1t.web.app

[gemini-code-assist]

Code Review

This pull request updates the documentation to support iOS 27 and macOS 27 (Golden Gate). Key changes include updating supported platform versions, adding a warning regarding macOS Intel (x64) deprecation, documenting the mandatory UIScene lifecycle starting with Xcode 27, and removing the obsolete "Flutter on latest iOS" page in favor of redirects. Feedback was provided to reword a sentence in the iOS setup guide to avoid using the first-person pronoun "we", aligning with the style guidelines.

[jmagman]

Some small comments. @vashworth should also review.

[sfshaza2]

I have a couple textual recommendations. But, in order to expedite this, I will approve, but don't land until engineering approves.

[MuthuGCodes]

Thanks a lot, @jmagman, @sfshaza2. I've incorporated the changes.

[jmagman]

The "crash on startup" part was important. How about:

Suggested change

	Beginning with Xcode 27 (iOS 27 SDK),
	Apple mandates the `UIScene` lifecycle for UIKit apps.
	Flutter apps that haven't adopted the `UIScene` lifecycle
	will crash on startup when built with Xcode 27 (iOS 27 SDK).

[jmagman]

This LGTM with the one nit about leaving in the "crash on startup" note.

Please hold off landing this until Monday when iOS 27 will be released.

Thank you!

[MuthuGCodes]

Thank you @jmagman. I've made the change.

I'll hold off landing this until Monday. Thanks a lot :)