Another attempt at #59009.
#72761 was reverted with #73437. This commit is the same, except it's now on top of #73442 which should resolve the infra issue where the devicelab agents' CocoaPods spec repo was too old.

Description

Swift packages cannot be added to a newly created Flutter iOS app due to the Xcode project settings (not workspace) being set to the "legacy" build location. Update to the "default" Xcode build location.

Update templates, add tool migrator, let tool upgrade all examples and integration tests.

Related Issues

Fixes #57083
Related to #49654
Unblocks #72482

Redux of #59009

Tests

• Migrator tests

Checklist

• I read the [Contributor Guide] and followed the process outlined there for submitting PRs.
• I signed the [CLA].
• I read and followed the [Flutter Style Guide], including [Features we expect every widget to implement].
• I read the [Tree Hygiene] wiki page, which explains my responsibilities.
• I updated/added relevant documentation (doc comments with ///).
• All existing and new tests are passing.
• The analyzer (flutter analyze --flutter-repo) does not report any problems on my PR.
• I am willing to follow-up on review comments in a timely manner.

Breaking Change

• 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.