feat(Skeleton): add @skeleton-avatar-size less var (#7556)

src/skeleton/index.tsx

@@ -96,6 +96,7 @@ Skeleton.props = {
   title: Boolean,
   round: Boolean,
   avatar: Boolean,
+  avatarSize: [Number, String],
   row: {
     type: [Number, String],
     default: 0,
@@ -108,10 +109,6 @@ Skeleton.props = {
     type: Boolean,
     default: true,
   },
-  avatarSize: {
-    type: [Number, String],
-    default: '32px',
-  },
   avatarShape: {
     type: String,
     default: 'round',