Generate XCFramework in recipe package script

[jmagman]

Description

Create Flutter.xcframework as part of the recipe packaging script.

Next steps

• Update the recipe to upload the generated Flutter.xcframework in that recipe to publish Flutter.xcframework as a downloadable engine artifact.
• Add it to the codesigning script.
• Update flutter tooling to use Flutter.xcframework.

Related Issues

Local engine support part of flutter/flutter#60109, which is a dependency to support macOS ARM simulators flutter/flutter#64502

Tests

The create_xcframework.py change is tested via the Scenario app, which embeds the Flutter.xcframework from the out directory and won't compile if something goes wrong there.

The create_xcframework.py output is only used in the recipe, and tested there. There are also many framework tests validating framework validation, bitcode, symbol stripping, etc, and this will be tested there when the tool adopts.

Checklist

• I read the [contributor guide] and followed the process outlined there for submitting PRs.
• I signed the [CLA].
• I read and followed the [C++, Objective-C, Java style guides] for the engine.
• I read the [tree hygiene] wiki page, which explains my responsibilities.
• I updated/added relevant documentation.
• All existing and new tests are passing.
• I am willing to follow-up on review comments in a timely manner.

Reviewer Checklist

• I have submitted any presubmit flakes in this PR using the [engine presubmit flakes form] before re-triggering the failure.

Breaking Change

Did any tests fail when you ran them? Please read [handling breaking changes].

• No, no existing tests failed, so this is not a breaking change.
• Yes, this is a breaking change. If not, delete the remainder of this section.

[dnfield]

LGTM