Use URLComponents to build the preview server URL

This allows us to supply the scheme, host and port independently, rather
than interpolating them into a string which we then parse.

Author: tomstuart

Sources/SwiftDocCUtilities/Action/Actions/PreviewAction.swift

@@ -163,7 +163,11 @@ public final class PreviewAction: Action, RecreatingContext {
         // Preview the output and monitor the source bundle for changes.
         do {
             print(String(repeating: "=", count: 40), to: &logHandle)
-            if let previewURL = URL(string: "http://localhost:\(port)") {
+            var components = URLComponents()
+            components.scheme = "http"
+            components.host = "localhost"
+            components.port = port
+            if let previewURL = components.url {
                 print("Starting Local Preview Server", to: &logHandle)
                 printPreviewAddresses(base: previewURL)
                 print(String(repeating: "=", count: 40), to: &logHandle)