patch 8.1.1933: the eval.c file is too big

Problem:    The eval.c file is too big.
Solution:   Move code related to variables to evalvars.c. (Yegappan
            Lakshmanan, closes #4868)
diff --git a/src/vim.h b/src/vim.h
index dca8748..1875e3b 100644
--- a/src/vim.h
+++ b/src/vim.h
@@ -2003,6 +2003,8 @@
 #define VAR_TYPE_CHANNEL    9
 #define VAR_TYPE_BLOB	    10
 
+#define DICT_MAXNEST 100	/* maximum nesting of lists and dicts */
+
 #ifdef FEAT_CLIPBOARD
 
 /* VIM_ATOM_NAME is the older Vim-specific selection type for X11.  Still