Fix undo bug

When recalling a line from history multiple times
and making edits to that line, the undo stack was incorrect.

The fix was to make a copy of the undo stack when recalling
from history.

Example repro:
    ls Enter
    UpArrow Escape dir Enter
    UpArrow UpArrow Escape

Author: lzybkr

PSReadLine/History.cs

@@ -262,7 +262,7 @@ private void UpdateFromHistory(bool moveCursor)
             else
             {
                 line = _history[_currentHistoryIndex]._line;
-                _edits = _history[_currentHistoryIndex]._edits;
+                _edits = new List<EditItem>(_history[_currentHistoryIndex]._edits);
                 _undoEditIndex = _history[_currentHistoryIndex]._undoEditIndex;
             }
             _buffer.Clear();