[native_assets_cli] `HookConfig` should have a `targetIosVersion`

[dcharkes]

trafficstars

Context:

• https://github.com/flutter/flutter/issues/148044

This would enable build and link hooks to fail if they cannot produce native code assets with that iOS SDK version.

Standalone Dart packages do not specify a minimum iOS version unlike Flutter plugins. Instead the flow with standalone packages with native assets is to get the ios target version as config value from the Flutter tools invocation.

[dcharkes]

Maybe xcodebuild can also consume a desired ios target version. Then we also want to plumb it through in package:native_toolchain_c.