feat(Field): add extra slot (#6290)

* feat(Field): add extra slot

* docs: remove form demo style

src/field/test/__snapshots__/index.spec.js.snap

@@ -79,6 +79,14 @@ exports[`reach max word-limit 1`] = `
 </div>
 `;
 
+exports[`render extra slot 1`] = `
+<div class="van-cell van-field">
+  <div class="van-cell__value van-cell__value--alone van-field__value">
+    <div class="van-field__body"><input type="text" class="van-field__control"></div>
+  </div>Extra
+</div>
+`;
+
 exports[`render input slot 1`] = `
 <div class="van-cell van-field">
   <div class="van-cell__value van-cell__value--alone van-field__value">

src/field/test/index.spec.js

@@ -203,14 +203,9 @@ test('clearable', () => {
 });
 
 test('render input slot', () => {
-  const wrapper = mount({
-    template: `
-      <field>
-        <template v-slot:input>Custom Input</template>
-      </field>
-    `,
-    components: {
-      Field,
+  const wrapper = mount(Field, {
+    scopedSlots: {
+      input: () => 'Custom Input',
     },
   });
 
@@ -218,14 +213,19 @@ test('render input slot', () => {
 });
 
 test('render label slot', () => {
-  const wrapper = mount({
-    template: `
-      <field label="Default Label">
-        <template v-slot:label>Custom Label</template>
-      </field>
-    `,
-    components: {
-      Field,
+  const wrapper = mount(Field, {
+    scopedSlots: {
+      label: () => 'Custom Label',
+    },
+  });
+
+  expect(wrapper).toMatchSnapshot();
+});
+
+test('render extra slot', () => {
+  const wrapper = mount(Field, {
+    scopedSlots: {
+      extra: () => 'Extra',
     },
   });