feat: bring back Video#is_live and add ExpandableMetadata (#256)

* bring back `Video#is_live`

* add ExpandableMetadata

src/parser/classes/ExpandableMetadata.ts

@@ -0,0 +1,41 @@
+import Parser from '..';
+
+import Text from './misc/Text';
+import Thumbnail from './misc/Thumbnail';
+
+import Button from './Button';
+import HorizontalCardList from './HorizontalCardList';
+
+import { YTNode } from '../helpers';
+
+class ExpandableMetadata extends YTNode {
+  static type = 'ExpandableMetadata';
+
+  header: {
+    collapsed_title: Text;
+    collapsed_thumbnail: Thumbnail[];
+    collapsed_label: Text;
+    expanded_title: Text;
+  };
+
+  expanded_content: HorizontalCardList | null;
+  expand_button: Button | null;
+  collapse_button: Button | null;
+
+  constructor(data: any) {
+    super();
+
+    this.header = {
+      collapsed_title: new Text(data.header.collapsedTitle),
+      collapsed_thumbnail: Thumbnail.fromResponse(data.header.collapsedThumbnail),
+      collapsed_label: new Text(data.header.collapsedLabel),
+      expanded_title: new Text(data.header.expandedTitle)
+    };
+
+    this.expanded_content = Parser.parseItem<HorizontalCardList>(data.expandedContent);
+    this.expand_button = Parser.parseItem<Button>(data.expandButton);
+    this.collapse_button = Parser.parseItem<Button>(data.collapseButton);
+  }
+}
+
+export default ExpandableMetadata;