[api] Update /api/examples/list to be static for vc init (#7596)

Previously, this API would download the entire git repository for each request. Instead, we can defer downloading to the `/download` API only and change the list API to be statically generated at build time.

This will improve the time to render the results from `vc init`.


## Before
- `https://vercel-lu6z5kf4s.vercel.sh/api/examples/list` responds in 6200 ms
- `https://vercel-lu6z5kf4s.vercel.sh/api/examples/list-all` responds in 800ms

## After
- `https://vercel-ctsxcwzgc.vercel.sh/api/examples/list` responds in 60 ms 
- `https://vercel-ctsxcwzgc.vercel.sh/api/examples/list-all` responds in 60 ms

api/_lib/script/build.ts

@@ -0,0 +1,46 @@
+import fs from 'fs/promises';
+import { join } from 'path';
+import { getExampleList } from '../examples/example-list';
+import { mapOldToNew } from '../examples/map-old-to-new';
+
+const repoRoot = join(__dirname, '..', '..', '..');
+const pubDir = join(repoRoot, 'public');
+
+async function main() {
+  console.log(`Building static frontend ${repoRoot}...`);
+
+  await fs.rm(pubDir, { recursive: true, force: true });
+  await fs.mkdir(pubDir);
+
+  const examples = await getExampleList();
+  const pathListAll = join(pubDir, 'list-all.json');
+  await fs.writeFile(pathListAll, JSON.stringify(examples));
+
+  const exampleDirs = await fs.readdir(join(repoRoot, 'examples'), {
+    withFileTypes: true,
+  });
+
+  const existingExamples = exampleDirs
+    .filter(dir => dir.isDirectory())
+    .map(dir => ({
+      name: dir.name,
+      visible: true,
+      suggestions: [],
+    }));
+
+  const oldExamples = Object.keys(mapOldToNew).map(key => ({
+    name: key,
+    visible: false,
+    suggestions: mapOldToNew[key],
+  }));
+
+  const pathList = join(pubDir, 'list.json');
+  await fs.writeFile(
+    pathList,
+    JSON.stringify([...existingExamples, ...oldExamples])
+  );
+
+  console.log('Completed building static frontend.');
+}
+
+main().catch(console.error);