feat(Tag): add closeable prop (#4763)

src/tag/index.less

@@ -1,7 +1,8 @@
 @import '../style/var';
 
 .van-tag {
-  display: inline-block;
+  display: inline-flex;
+  align-items: center;
   padding: @tag-padding;
   color: @tag-text-color;
   font-size: @tag-font-size;
@@ -58,19 +59,18 @@
   }
 
   &--mark {
-    padding-right: .6em;
-    border-radius: 0 .8em .8em 0;
+    padding-right: .7em;
 
+    &,
     &::after {
-      border-radius: 0 1.6em 1.6em 0;
+      border-radius: 0 @tag-round-border-radius @tag-round-border-radius 0;
     }
   }
 
   &--round {
-    border-radius: @tag-round-border-radius;
-
+    &,
     &::after {
-      border-radius: @tag-round-border-radius * 2;
+      border-radius: @tag-round-border-radius;
     }
   }
 
@@ -81,4 +81,8 @@
   &--large {
     font-size: @tag-large-font-size;
   }
+
+  &__close {
+    margin-left: 2px;
+  }
 }