feat(ui-shell): add Header skip-to-main-content slot

src/UIShell/GlobalHeader/Header.svelte

@@ -43,6 +43,7 @@
 <svelte:window bind:innerWidth={winWidth} />
 
 <header role="banner" aria-label={ariaLabel} class:bx--header={true}>
+  <slot name="skip-to-main-content" />
   {#if winWidth < 1056}
     <HamburgerMenu bind:isOpen={isSideNavOpen} />
   {/if}

src/UIShell/UIShell.Story.svelte

@@ -129,7 +129,9 @@
 
 {#if story === 'header'}
   <Header {...$$props} company={undefined}>
-    <SkipToContent />
+    <div slot="skip-to-main-content">
+      <SkipToContent />
+    </div>
     <span slot="platform" class="platform-name">
       Platform Name
       <small>1.12.2</small>