chore: add vant-doc package (#4197)

packages/vant-doc/src/component/DemoSection.vue

@@ -0,0 +1,62 @@
+<template>
+  <section class="van-doc-demo-section" :class="`demo-${demoName}`" :style="style">
+    <slot />
+  </section>
+</template>
+
+<script>
+export default {
+  name: 'van-doc-demo-section',
+
+  props: {
+    name: String,
+    title: String,
+    background: String
+  },
+
+  computed: {
+    demoName() {
+      return this.name || this.getParentName();
+    },
+    style() {
+      return {
+        background: this.background
+      };
+    }
+  },
+
+  methods: {
+    getParentName() {
+      const { $parent } = this;
+      if ($parent && $parent.$options.name) {
+        return $parent.$options.name.replace('demo-', '');
+      }
+    }
+  }
+};
+</script>
+
+<style lang="less">
+@import '../style/variable';
+
+.van-doc-demo-section {
+  box-sizing: border-box;
+  min-height: 100vh;
+  padding-bottom: 20px;
+
+  &__title {
+    margin: 0;
+    padding: 15px;
+    font-weight: normal;
+    font-size: 16px;
+    line-height: 1.5;
+    text-transform: capitalize;
+
+    + .van-doc-demo-block {
+      .van-doc-demo-block__title {
+        padding-top: 0;
+      }
+    }
+  }
+}
+</style>