data tree CHANGE provide lyd_is_default()

Rename internal ly_is_default() to lyd_is_default() and make it public
as a replacement for lyd_wd_default() from libyang 1.x.
diff --git a/src/printer_lyb.c b/src/printer_lyb.c
index 1aa2314..d90fc9d 100644
--- a/src/printer_lyb.c
+++ b/src/printer_lyb.c
@@ -699,7 +699,7 @@
     /* with-defaults */
     if (node->schema->nodetype & LYD_NODE_TERM) {
         if (((node->flags & LYD_DEFAULT) && (lybctx->print_options & (LYD_PRINT_WD_ALL_TAG | LYD_PRINT_WD_IMPL_TAG))) ||
-                ((lybctx->print_options & LYD_PRINT_WD_ALL_TAG) && ly_is_default(node))) {
+                ((lybctx->print_options & LYD_PRINT_WD_ALL_TAG) && lyd_is_default(node))) {
             /* we have implicit OR explicit default node, print attribute only if context include with-defaults schema */
             wd_mod = ly_ctx_get_module_latest(node->schema->module->ctx, "ietf-netconf-with-defaults");
         }