fix(#618): Add ExternalLink icon to GitHub Repo chip (#625)

In this PR:

- Add `ExternalLink` icon, sourced from [Hero
Icons](https://heroicons.dev/)
- Append `ExternalLink` icon to the GitHub repo chip on
`routes/package/(_components)/PackageHeader.tsx` to help signify that
it's an external link, which should at least partially resolve #618

<img width="1407" alt="Screenshot 2024-07-01 at 12 12 25 PM"
src="https://github.com/jsr-io/jsr/assets/35377827/8d189e23-b412-4a45-bec3-395c697f4527">
<img width="612" alt="Screenshot 2024-07-01 at 12 12 21 PM"
src="https://github.com/jsr-io/jsr/assets/35377827/acc69b71-12c5-4e25-b1c9-723c74eb2bc1">

Author: alectrocute

frontend/components/icons/ExternalLink.tsx

@@ -0,0 +1,19 @@
+// Copyright 2024 the JSR authors. All rights reserved. MIT license.
+export function ExternalLink(props: { class?: string; strokeWidth?: string }) {
+  return (
+    <svg
+      fill="none"
+      stroke-width={props.strokeWidth ?? "1.5"}
+      stroke="currentColor"
+      viewBox="0 0 24 24"
+      xmlns="http://www.w3.org/2000/svg"
+      class={`size-4 ${props.class ?? ""}`}
+    >
+      <path
+        stroke-linecap="round"
+        stroke-linejoin="round"
+        d="M13.5 6H5.25A2.25 2.25 0 0 0 3 8.25v10.5A2.25 2.25 0 0 0 5.25 21h10.5A2.25 2.25 0 0 0 18 18.75V10.5m-10.5 6L21 3m0 0h-5.25M21 3v5.25"
+      />
+    </svg>
+  );
+}

frontend/routes/package/(_components)/PackageHeader.tsx

@@ -1,5 +1,6 @@
 // Copyright 2024 the JSR authors. All rights reserved. MIT license.
 import { Package, PackageVersionWithUser } from "../../../utils/api_types.ts";
+import { ExternalLink } from "../../../components/icons/ExternalLink.tsx";
 import { GitHub } from "../../../components/icons/GitHub.tsx";
 import { RuntimeCompatIndicator } from "../../../components/RuntimeCompatIndicator.tsx";
 import { getScoreTextColorClass } from "../../../utils/score_ring_color.ts";
@@ -141,6 +142,7 @@ export function PackageHeader(
                   <span>
                     {pkg.githubRepository.owner}/{pkg.githubRepository.name}
                   </span>
+                  <ExternalLink strokeWidth="2.25" />
                 </a>
               )}
             </div>