Use wxArrayInt methods instead of duplicating them.

Just use wxArrayInt::Index() instead of doing a linear search in the array
manually. Also use RemoveAt() + Insert() instead of manually iterating over
the items.

See #16110.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@76454 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

include/wx/generic/grid.h

@@ -1448,15 +1448,10 @@ public:
         if ( m_colAt.IsEmpty() )
             return idx;
 
-        for ( int i = 0; i < m_numCols; i++ )
-        {
-            if ( m_colAt[i] == idx )
-                return i;
-        }
+        int pos = m_colAt.Index(idx);
+        wxASSERT_MSG( pos != wxNOT_FOUND, "invalid column index" );
 
-        wxFAIL_MSG( "invalid column index" );
-
-        return wxNOT_FOUND;
+        return pos;
     }
 
     // reset the columns positions to the default order