Experimentally expose RubyVM::AST::Node#node_id

Now ISeq#to_a includes the node_id list for each bytecode instruction.
I want a way to retrieve the AST::Node instance corresponding to an
instruction for a research purpose including TypeProf-based LSP server.

ast.c

@@ -254,16 +254,14 @@ ast_node_type(rb_execution_context_t *ec, VALUE self)
     return rb_sym_intern_ascii_cstr(node_type_to_str(data->node));
 }
 
-#ifdef DEBUG_ISEQ_NODE_ID
 static VALUE
-ast_node_node_id(VALUE self)
+ast_node_node_id(rb_execution_context_t *ec, VALUE self)
 {
     struct ASTNodeData *data;
     TypedData_Get_Struct(self, struct ASTNodeData, &rb_node_type, data);
 
     return INT2FIX(nd_node_id(data->node));
 }
-#endif
 
 #define NEW_CHILD(ast, node) node ? ast_new_internal(ast, node) : Qnil
 
@@ -725,7 +723,4 @@ Init_ast(void)
     rb_mAST = rb_define_module_under(rb_cRubyVM, "AbstractSyntaxTree");
     rb_cNode = rb_define_class_under(rb_mAST, "Node", rb_cObject);
     rb_undef_alloc_func(rb_cNode);
-#ifdef DEBUG_ISEQ_NODE_ID
-    rb_define_method(rb_cNode, "node_id", ast_node_node_id, 0);
-#endif
 }

ast.rb

@@ -140,6 +140,17 @@ module RubyVM::AbstractSyntaxTree
       Primitive.ast_node_inspect
     end
 
+    #  call-seq:
+    #     node.node_id -> integer
+    #
+    #  Returns an internal node_id number.
+    #  Note that this is an API for ruby internal use, debugging,
+    #  and research. Do not use this for any other purpose.
+    #  The compatibility is not guaranteed.
+    def node_id
+      Primitive.ast_node_node_id
+    end
+
     #  call-seq:
     #     node.script_lines -> array
     #