Review feedback: use only Foundation instead of stdio functions for writing data back to SwiftPM

Author: abertelrud

Sources/PackagePlugin/Implementation.swift

@@ -68,12 +68,12 @@ extension Plugin {
             }
         }
 
-        // Emit the output from the plugin for SwiftPM to read.
+        // Encoding the output struct from the plugin for SwiftPM to read.
         let encoder = JSONEncoder()
         let outputData = try! encoder.encode(output)
-        fputc(0, stdout)
-        fputs(String(data: outputData, encoding: .utf8)!, stdout)
-        fflush(stdout)
+        
+        // On stdout, write a zero byte followed by the JSON data — this is what libSwiftPM expects to see. Anything before the last zero byte is treated as freeform output from the plugin (such as debug output from `print` statements).
+        FileHandle.standardOutput.write(Data([0]) + outputData)
     }
 }