Moved logic to get the Xcode's expansion directory to a function inside Files

As suggested by @MattKiazyk, to be able to get the expansion directory by simply calling `Current.files.xcodeExpansionDirectory()`.

- The `Files.temporalDirectory()` added on the previous commits is keep even if it's not used outside `Files.xcodeExpansionDirectory()`, to keep each function with a single statement (as the other functions on `Files`).
- I'm not sure there's value on adding the `xcodeExpansionDirectory` variable, but added for consistency with the other functions on `Files`.

Author: juanjonol

Sources/XcodesKit/Environment.swift

@@ -244,6 +244,12 @@ public struct Files {
         return try temporalDirectory(URL)
     }
 
+    public var xcodeExpansionDirectory: (URL, URL) -> URL = { (try? Current.files.temporalDirectory(for: $1)) ?? $0.deletingLastPathComponent() }
+
+    public func xcodeExpansionDirectory(archiveURL: URL, xcodeURL: URL) -> URL {
+        return xcodeExpansionDirectory(archiveURL, xcodeURL)
+    }
+
     public var installedXcodes = XcodesKit.installedXcodes
 }
 private func installedXcodes(directory: Path) -> [InstalledXcode] {

Sources/XcodesKit/XcodeInstaller.swift

@@ -718,7 +718,7 @@ public final class XcodeInstaller {
     }
 
     func unarchiveAndMoveXIP(at source: URL, to destination: URL) -> Promise<URL> {
-        let xcodeExpansionDirectory = (try? Current.files.temporalDirectory(for: destination)) ?? source.deletingLastPathComponent()
+        let xcodeExpansionDirectory = Current.files.xcodeExpansionDirectory(archiveURL: source, xcodeURL: destination)
         return firstly { () -> Promise<ProcessOutput> in
             Current.logging.log(InstallationStep.unarchiving.description)
             return Current.shell.unxip(source, xcodeExpansionDirectory)

Tests/XcodesKitTests/Environment+Mock.swift

@@ -61,6 +61,7 @@ extension Files {
         createFile: { _, _, _ in return true },
         createDirectory: { _, _, _ in },
         temporalDirectory: { _ in return URL(fileURLWithPath: NSTemporaryDirectory()) },
+        xcodeExpansionDirectory: { _, _ in return URL(fileURLWithPath: NSTemporaryDirectory()) },
         installedXcodes: { _ in [] }
     )
 }