Fix symlinked swift-experimental-destination invocations

`swift experimental-destination` subcommands no longer work and always display help output. This is a regression introduced in #6362 after making `SwiftDestinationTool` conform to  `AsyncParsableCommand` instead of `ParsableCommand` but not updating `swift-package-manager` command sources to call `async` overload of `main()` function on `SwiftDestinationTool`.

rdar://107618266

Author: MaxDesiatov

Sources/swift-package-manager/SwiftPM.swift

@@ -22,14 +22,14 @@ let execName = (try? AbsolutePath(validating: firstArg).basenameWithoutExt) ??
 
 @main
 struct SwiftPM {
-    static func main() {
+    static func main() async {
         switch execName {
         case "swift-package":
             SwiftPackageTool.main()
         case "swift-build":
             SwiftBuildTool.main()
         case "swift-experimental-destination":
-            SwiftDestinationTool.main()
+            await SwiftDestinationTool.main()
         case "swift-test":
             SwiftTestTool.main()
         case "swift-run":