docs: add target blank for all links (#5073)

packages/vant-markdown-loader/src/link-open.js

@@ -0,0 +1,18 @@
+// add target="_blank" to all links
+module.exports = function linkOpen(md) {
+  const defaultRender =
+    md.renderer.rules.link_open ||
+    function(tokens, idx, options, env, self) {
+      return self.renderToken(tokens, idx, options);
+    };
+
+  md.renderer.rules.link_open = function(tokens, idx, options, env, self) {
+    const aIndex = tokens[idx].attrIndex('target');
+
+    if (aIndex < 0) {
+      tokens[idx].attrPush(['target', '_blank']); // add new attribute
+    }
+
+    return defaultRender(tokens, idx, options, env, self);
+  };
+};