breaking(ui-shell): remove GlobalHeader, SideNav folders (#1223)

* breaking(ui-shell): remove GlobalHeader/SideNav folders

* Run "yarn build:docs"

src/UIShell/SideNavMenuItem.svelte

@@ -0,0 +1,32 @@
+<script>
+  /** Set to `true` to select the item */
+  export let isSelected = false;
+
+  /**
+   * Specify the `href` attribute
+   * @type {string}
+   */
+  export let href = undefined;
+
+  /**
+   * Specify the item text
+   * @type {string}
+   */
+  export let text = undefined;
+
+  /** Obtain a reference to the HTML anchor element */
+  export let ref = null;
+</script>
+
+<li class:bx--side-nav__menu-item="{true}">
+  <a
+    bind:this="{ref}"
+    aria-current="{isSelected ? 'page' : undefined}"
+    href="{href}"
+    class:bx--side-nav__link="{true}"
+    {...$$restProps}
+    on:click
+  >
+    <span class:bx--side-nav__link-text="{true}"><slot>{text}</slot></span>
+  </a>
+</li>