feat(dropdown): [dropdown] add right side expansion

Author: MomoPoppy

examples/sites/demos/apis/dropdown.js

@@ -371,7 +371,10 @@ export default {
             'en-US': 'Menu pop-up location '
           },
           mode: ['pc'],
-          pcDemo: 'basic-usage'
+          pcDemo: 'basic-usage',
+          meta: {
+            experimental: '3.21.0'
+          }
         },
         {
           name: 'popper-class',

packages/theme/src/dropdown-item/index.less

@@ -14,6 +14,7 @@
 @import './vars.less';
 
 @dropdown-item-prefix-cls: ~'@{css-prefix}dropdown-item';
+@dropdown-menu-prefix-cls: ~'@{css-prefix}dropdown-menu';
 @svg-prefix-cls: ~'@{css-prefix}svg';
 
 .@{dropdown-item-prefix-cls} {
@@ -157,11 +158,11 @@
 }
 
 /* 右侧展开 */
-.tiny-dropdown-menu[x-placement='bottom-start'],
-.tiny-dropdown-menu[x-placement='top-start'] {
+.@{dropdown-menu-prefix-cls}[x-placement='bottom-start'],
+.@{dropdown-menu-prefix-cls}[x-placement='top-start'] {
   &:has(.has-children) {
     &,
-    .tiny-dropdown-menu {
+    .@{dropdown-menu-prefix-cls} {
       & > li:not(.has-children) .@{dropdown-item-prefix-cls}__content {
         margin-left: 0;
       }