refactor: Convert the build scripts to TypeScript and group them (#2696)

- Closes: #2695

scripts/vitest/browsers.ts

@@ -0,0 +1,27 @@
+const BROWSERS = ['chromium', 'firefox', 'webkit'] as const;
+
+export type Browser = (typeof BROWSERS)[number];
+
+const isValidBrowser = (name: string): name is Browser =>
+  BROWSERS.some((browser) => browser === name);
+
+/**
+ * Which browsers to run, all of them unless one is named. CI names one per job
+ * so that the three run at the same time on separate machines rather than one
+ * after another on one.
+ *
+ * Shared by every suite that mounts the card, so that naming a browser means
+ * the same thing to each of them.
+ */
+export const getBrowsers = (): readonly Browser[] => {
+  const requested = process.env.VITEST_BROWSER;
+  if (requested === undefined) {
+    return BROWSERS;
+  }
+
+  if (!isValidBrowser(requested)) {
+    throw new Error(`Unknown browser: ${requested}`);
+  }
+
+  return [requested];
+};