fix(Field): 修复全局设置 user-select: none 时 IOS 下无法输入的问题 (#9418)

* fix: 修复IOS输入光标不显示无法输入内容

* Update index.less

Co-authored-by: neverland <chenjiahan@buaa.edu.cn>

packages/vant/src/field/index.less

@@ -78,6 +78,8 @@
     background-color: transparent;
     border: 0;
     resize: none;
+    // https://github.com/youzan/vant/pull/9418
+    user-select: auto;
 
     &::placeholder {
       color: var(--van-field-placeholder-text-color);