[5.9] Preserve port when computing the login URL

[Palleas]

(Same as #6711 but for 5.9.)

When using a registry URL that contains a port, ensure the port is preserved when computing the login URL.

Motivation:

Currently if you run the following

swift package-registry set https://packages.example.com:8081
swift package-registry login --token XYZ

You might get something like

Error: Unable to connect to server: https://packages.example.com

That's because the login url is built like this and ignores the port: URL(string: "https://\(host)\(loginAPIPath ?? "/login")")

Modifications:

• Use URLComponents to build the login URL (which maintains the port)
• Update RegistryConfiguration to compute the storage key

Result:

SPM can use registry URLs with ports.

[Palleas]

@swift-ci please test

[yim-lee]

@swift-ci please smoke test