Initial commit with files

Still need to fix the imports

src/lib/components/portal/Portal.svelte

@@ -0,0 +1,29 @@
+<script lang="ts">
+    import { usePortalGroupContext } from "./PortalGroup.svelte";
+    import { usePortalRoot } from "./ForcePortalRootContext.svelte";
+    import { portal } from "./use-portal";
+    let forceInRoot = usePortalRoot();
+    let groupTarget = usePortalGroupContext();
+    $: target = (() => {
+        // Group context is used, but still null
+        if (
+            !(forceInRoot && $forceInRoot) &&
+            groupTarget !== undefined &&
+            $groupTarget !== null
+        )
+            return $groupTarget;
+
+        // No group context is used, let's create a default portal root
+        if (typeof window === "undefined") return null;
+        let existingRoot = document.getElementById("headlessui-portal-root");
+        if (existingRoot) return existingRoot;
+
+        let root = document.createElement("div");
+        root.setAttribute("id", "headlessui-portal-root");
+        return document.body.appendChild(root);
+    })();
+</script>
+
+<div use:portal={target}>
+    <slot />
+</div>