[refactoring] update ast structure of "StmtList" nodes

pkg/ast/node.go

@@ -691,7 +691,9 @@ func (n *StmtStaticVar) Accept(v NodeVisitor) {
 // StmtStmtList node
 type StmtStmtList struct {
 	Node
-	Stmts []Vertex
+	OpenCurlyBracket  *token.Token
+	Stmts             []Vertex
+	CloseCurlyBracket *token.Token
 }
 
 func (n *StmtStmtList) Accept(v NodeVisitor) {

pkg/ast/visitor/filter_tokens.go

@@ -82,3 +82,8 @@ func (v *FilterTokens) StmtConstant(n *ast.StmtConstant) {
 	n.EqualTkn = nil
 	n.CommaTkn = nil
 }
+
+func (v *FilterTokens) StmtStmtList(n *ast.StmtStmtList) {
+	n.OpenCurlyBracket = nil
+	n.CloseCurlyBracket = nil
+}