style(Picker): add @picker-option-height less var (#6571)

src/picker/PickerColumn.js

@@ -3,6 +3,7 @@ import { createNamespace, isObject } from '../utils';
 import { range } from '../utils/format/number';
 import { preventDefault } from '../utils/dom/event';
 import { TouchMixin } from '../mixins/touch';
+import { DEFAULT_ITEM_HEIGHT } from './shared';
 
 const DEFAULT_DURATION = 200;
 
@@ -255,9 +256,11 @@ export default createComponent({
     },
 
     genOptions() {
-      const optionStyle = {
-        height: `${this.itemHeight}px`,
-      };
+      const optionStyle = {};
+
+      if (this.itemHeight !== DEFAULT_ITEM_HEIGHT) {
+        optionStyle.height = `${this.itemHeight}px`;
+      }
 
       return this.options.map((option, index) => {
         const text = this.getOptionText(option);