style: decentralized less var (#8369)

* style: decentralized less var

* chore: remove emtpy var file

src/toast/index.less

@@ -1,4 +1,4 @@
-@import '../style/var.less';
+@import './var.less';
 
 .van-toast {
   display: flex;

src/toast/var.less

@@ -0,0 +1,17 @@
+@import '../style/var.less';
+
+@toast-max-width: 70%;
+@toast-font-size: @font-size-md;
+@toast-text-color: @white;
+@toast-loading-icon-color: @white;
+@toast-line-height: @line-height-md;
+@toast-border-radius: @border-radius-lg;
+@toast-background-color: fade(@black, 70%);
+@toast-icon-size: 36px;
+@toast-text-min-width: 96px;
+@toast-text-padding: @padding-xs @padding-sm;
+@toast-default-padding: @padding-md;
+@toast-default-width: 88px;
+@toast-default-min-height: 88px;
+@toast-position-top-distance: 20%;
+@toast-position-bottom-distance: 20%;