patch 8.0.0457: using :move messes up manual folds

Problem:    Using :move messes up manual folds.
Solution:   Split adjusting marks and folds.  Add foldMoveRange(). (neovim
            patch #6221)
diff --git a/src/proto/fold.pro b/src/proto/fold.pro
index dce1803..cda536b 100644
--- a/src/proto/fold.pro
+++ b/src/proto/fold.pro
@@ -31,6 +31,7 @@
 int find_wl_entry(win_T *win, linenr_T lnum);
 void foldAdjustVisual(void);
 void foldAdjustCursor(void);
+void foldMoveRange(garray_T *gap, linenr_T line1, linenr_T line2, linenr_T dest);
 void cloneFoldGrowArray(garray_T *from, garray_T *to);
 void deleteFoldRecurse(garray_T *gap);
 void foldMarkAdjust(win_T *wp, linenr_T line1, linenr_T line2, long amount, long amount_after);