perf[SizeSelect]: add default size option (#1566)

src/components/SizeSelect/index.vue

@@ -4,15 +4,24 @@
       <svg-icon class-name="size-icon" icon-class="size" />
     </div>
     <el-dropdown-menu slot="dropdown">
-      <el-dropdown-item :disabled="size==='medium'" command="medium">Medium</el-dropdown-item>
-      <el-dropdown-item :disabled="size==='small'" command="small">Small</el-dropdown-item>
-      <el-dropdown-item :disabled="size==='mini'" command="mini">Mini</el-dropdown-item>
+      <el-dropdown-item v-for="item of sizeOptions" :key="item.value" :disabled="size===item.value" :command="item.value">{{
+      item.label }}</el-dropdown-item>
     </el-dropdown-menu>
   </el-dropdown>
 </template>
 
 <script>
 export default {
+  data() {
+    return {
+      sizeOptions: [
+        { label: 'Default', value: 'default' },
+        { label: 'Medium', value: 'medium' },
+        { label: 'Small', value: 'small' },
+        { label: 'Mini', value: 'mini' }
+      ]
+    }
+  },
   computed: {
     size() {
       return this.$store.getters.size