feat(button-skeleton): add size prop consistent with Button

src/Button/Button.Skeleton.svelte

@@ -5,6 +5,12 @@
    */
   export let href = undefined;
 
+  /**
+   * Specify the size of button skeleton
+   * @type {"default" | "field" | "small"} [size="default"]
+   */
+  export let size = "default";
+
   /**
    * Set to `true` to use the small variant
    * @type {boolean} [small=false]
@@ -19,7 +25,8 @@
     role="button"
     class:bx--skeleton="{true}"
     class:bx--btn="{true}"
-    class:bx--btn--sm="{small}"
+    class:bx--btn--field="{size === 'field'}"
+    class:bx--btn--sm="{size === 'small' || small}"
     {...$$restProps}
     on:click
     on:mouseover
@@ -32,7 +39,8 @@
   <div
     class:bx--skeleton="{true}"
     class:bx--btn="{true}"
-    class:bx--btn--sm="{small}"
+    class:bx--btn--field="{size === 'field'}"
+    class:bx--btn--sm="{size === 'small' || small}"
     {...$$restProps}
     on:click
     on:mouseover

src/Button/Button.svelte

@@ -123,7 +123,7 @@
 {#if skeleton}
   <ButtonSkeleton
     href="{href}"
-    small="{size === 'small'}"
+    size="{size}"
     {...$$restProps}
     style="{hasIconOnly && 'width: 3rem;'}"
     on:click