SE-0292 (2nd review): Package Registry Service

[lukasa (Cory Benfield)]

@mattt

According to the current HEAD of main on apple/swift-package-manager (bbcfe08):

// --netrc-file option only supported on macOS >=10.13

Until .netrc is supported on all platforms, I don't think we can remove support for URL-encoded credentials.

This is supported on all platforms that matter. SPM doesn't back-deploy on macOS beyond 1 release, so will never need to run before 10.13, and the * means that it will safely run everywhere else.