libyang CHANGE use LY_ARRAY_SIZE_TYPE for iterator variables in LY_TREE_FOR

Because of the change in sized arrays design (780ade2101), also the
iterators and other variables used with LY_TREE_FOR or LY_TREE_SIZE
should be of LY_ARRAY_SIZE_TYPE.

Also the new LY_PRI_ARRAY_SIZE_TYPE was introduced to correctly print
the value of this type in a formatted print functions.
diff --git a/src/printer_xml.c b/src/printer_xml.c
index ce2136a..279d336 100644
--- a/src/printer_xml.c
+++ b/src/printer_xml.c
@@ -229,7 +229,7 @@
 {
     const struct ly_attr *attr;
     const char *pref;
-    uint32_t u;
+    LY_ARRAY_SIZE_TYPE u;
 
     LY_LIST_FOR(node->attr, attr) {
         pref = NULL;
@@ -429,7 +429,7 @@
 {
     LY_ERR ret;
     struct lyd_node *child;
-    uint32_t u;
+    LY_ARRAY_SIZE_TYPE u;
 
     LY_CHECK_RET(xml_print_opaq_open(ctx, node));