Support for `Package.resolved` version 3

[ed-irl]

A new Package.resolved format was seemingly released in xcode 15.3. The format seems to be the same for the purposes of the pins in my repo, which are all remote. I was able to resolve the issue by adding case 2, 3: in pin.go.

Since this type of upgrade happens more or less silently, it might be worth revising the error message in this file to be more informational, eg. instead of "unrecognized version %d for resolved package JSON" it could be "A new 'Package.resolved' format version %d was detected. This may happen when a new xcode version is released. Please report the new version at https://github.com/cgrindel/rules_swift_package_manager/issues. In the meantime, you can resolve this problem by using git_override to patch pin.go and the associated pin_store*.go files."