Use FSR for Process executable path on Windows (#4999)

* Use FSR for Process executable path on Windows

* Use FSR on Linux as well

Author: jmschonfeld

Sources/Foundation/Process.swift

@@ -499,7 +499,7 @@ open class Process: NSObject {
         }
 
 #if os(Windows)
-        var command: [String] = [launchPath]
+        var command: [String] = [try FileManager.default._fileSystemRepresentation(withPath: launchPath) { String(decodingCString: $0, as: UTF16.self) }]
         if let arguments = self.arguments {
           command.append(contentsOf: arguments)
         }
@@ -958,9 +958,12 @@ open class Process: NSObject {
 
         // Launch
         var pid = pid_t()
-        guard _CFPosixSpawn(&pid, launchPath, fileActions, &spawnAttrs, argv, envp) == 0 else {
-            throw _NSErrorWithErrno(errno, reading: true, path: launchPath)
-        }
+        
+        try FileManager.default._fileSystemRepresentation(withPath: launchPath, { fsRep in
+            guard _CFPosixSpawn(&pid, fsRep, fileActions, &spawnAttrs, argv, envp) == 0 else {
+                throw _NSErrorWithErrno(errno, reading: true, path: launchPath)
+            }
+        })
         posix_spawnattr_destroy(&spawnAttrs)
 
         // Close the write end of the input and output pipes.