Fix ReadLineWithTabCompletion port

Revert change made within the function since the function itself is
compiled out for the portable version of PowerShell.

src/Microsoft.PowerShell.ConsoleHost/host/msh/ConsoleHostUserInterface.cs

@@ -1823,9 +1823,13 @@ namespace Microsoft.PowerShell
         {
             string input = null;
             string lastInput = "";
-            string lastCompletion = "";
 
             ReadLineResult rlResult = ReadLineResult.endedOnEnter;
+
+#if !PORTABLE
+            ConsoleHandle handle = ConsoleControl.GetActiveScreenBufferHandle();
+
+            string lastCompletion = "";
             Size screenBufferSize = RawUI.BufferSize;
 
             // Save the cursor position at the end of the prompt string so that we can restore it later to write the
@@ -1835,6 +1839,7 @@ namespace Microsoft.PowerShell
 
             CommandCompletion commandCompletion = null;
             string completionInput = null;
+#endif
 
             do
             {
@@ -1845,9 +1850,6 @@ namespace Microsoft.PowerShell
 
                 input = ReadLine(true, lastInput, out rlResult, false, false);
 
-                Coordinates endOfInputCursorPos = RawUI.CursorPosition;
-                string completedInput = null;
-
                 if (input == null)
                 {
                     break;
@@ -1858,6 +1860,13 @@ namespace Microsoft.PowerShell
                     break;
                 }
 
+#if PORTABLE // Portable code only ends on enter (or no input), so tab is not processed
+                throw new PlatformNotSupportedException("This readline state is unsupported in portable code!");
+#else
+
+                Coordinates endOfInputCursorPos = RawUI.CursorPosition;
+                string completedInput = null;
+
                 if (rlResult == ReadLineResult.endedOnTab || rlResult == ReadLineResult.endedOnShiftTab)
                 {
                     int tabIndex = input.IndexOf(Tab, StringComparison.CurrentCulture);
@@ -1946,19 +1955,13 @@ namespace Microsoft.PowerShell
 
                     if (deltaInput > 0)
                     {
-                        Console.SetCursorPosition(endOfCompletionCursorPos.X, endOfCompletionCursorPos.Y);
-                        for (int i = 0; i < deltaInput; i++)
-                        {
-                            Console.Write(' ');
-                        }
+                        ConsoleControl.FillConsoleOutputCharacter(handle, ' ', deltaInput, endOfCompletionCursorPos);
                     }
 
                     if (restOfLine != string.Empty)
                     {
                         lastCompletion = completedInput.Remove(completedInput.Length - restOfLine.Length);
-#if !PORTABLE
                         SendLeftArrows(restOfLine.Length);
-#endif
                     }
                     else
                     {
@@ -1967,6 +1970,7 @@ namespace Microsoft.PowerShell
 
                     lastInput = completedInput;
                 }
+#endif
             }
             while (true);