This updates the flutter tool cache to download binary files for ideviceinstaller, ios-deploy, libimobiledevice, and dynamically linked dependencies from Flutter's GCP bucket.

This reverts commit 14d489ad.

This updates the flutter tool to cache binary files for ideviceinstaller, ios-deploy, libimobiledevice, and dynamically linked dependencies from Flutter's GCP bucket.

Splits Xcode validation out of the iOS validator and into a stand-alone
validator, and groups the CocoaPods validator with that top-level
validator instead of the iOS validator. iOS now validates only the
iOS-specific tools (e.g., ideviceinstaller).

Reorganizes many of the associated clases so that those that are used by
both macOS and iOS live in macos/ rather than ios/. Moves some
validators to their own files as part of the restructuring.

This is the macOS portion of #31368