feat: implement switchable task list node

plugin/gomark/ast/utils.go

@@ -0,0 +1,23 @@
+package ast
+
+func FindPrevSiblingExceptLineBreak(node Node) Node {
+	if node == nil {
+		return nil
+	}
+	prev := node.PrevSibling()
+	if prev != nil && prev.Type() == LineBreakNode {
+		return FindPrevSiblingExceptLineBreak(prev)
+	}
+	return prev
+}
+
+func FindNextSiblingExceptLineBreak(node Node) Node {
+	if node == nil {
+		return nil
+	}
+	next := node.NextSibling()
+	if next != nil && next.Type() == LineBreakNode {
+		return FindNextSiblingExceptLineBreak(next)
+	}
+	return next
+}