Fix 2 vi-mode cursor placement issues (#627)

Fix cursor placement after `cf`
Also fix cursor placement with `s` at EOL.

Fix #623

PSReadLine/ReadLine.vi.cs

@@ -576,7 +576,14 @@ namespace Microsoft.PowerShell
         public static void ViInsertWithDelete(ConsoleKeyInfo? key = null, object arg = null)
         {
             _singleton._groupUndoHelper.StartGroup(ViInsertWithDelete, arg);
+
+            var isEOL = _singleton._current == _singleton._buffer.Length + ViEndOfLineFactor;
+
             DeleteChar(key, arg);
+            if(isEOL)
+            {
+                _singleton._current++;
+            }
             ViInsertMode(key, arg);
         }
 

PSReadLine/Replace.vi.cs

@@ -250,13 +250,13 @@ namespace Microsoft.PowerShell
 
         private static void ViReplaceToChar(char keyChar, ConsoleKeyInfo? key = null, object arg = null)
         {
-            bool shouldAppend = _singleton._current > 0;
+            int initialCurrent = _singleton._current;
 
             _singleton._groupUndoHelper.StartGroup(ReplaceChar, arg);
             ViCharacterSearcher.Set(keyChar, isBackward: false, isBackoff: false);
             if (ViCharacterSearcher.SearchDelete(keyChar, arg, backoff: false, instigator: (_key, _arg) => ViReplaceToChar(keyChar, _key, _arg)))
             {
-                if (shouldAppend)
+                if (_singleton._current < initialCurrent || _singleton._current >= _singleton._buffer.Length)
                 {
                     ViInsertWithAppend(key, arg);
                 }

test/BasicEditingTest.VI.cs

@@ -90,6 +90,22 @@ namespace Test
                 ));
         }
 
+        [Fact]
+        public void ViDefect623()
+        {
+            TestSetup(KeyMode.Vi);
+
+            Test("012 4568", Keys(
+                "012 4567", _.Escape, CheckThat(() => AssertCursorLeftIs(7)),
+                "s8", _.Escape, CheckThat(() => AssertCursorLeftIs(7)), CheckThat(() => AssertLineIs("012 4568"))
+                ));
+
+            Test("asdf bzdf", Keys(
+                "asdf asdf", _.Escape, "0wcfs", CheckThat(() => AssertCursorLeftIs(5)),
+                "bz"
+                ));
+        }
+
         [Fact]
         public void ViChangeMovementUndo()
         {