chore: Move to Typescript (#2783)

This PR moves the entire project to Typescript. Due to the ~1000 ignores this will lead to a messy codebase for a while, but the churn is worth it – all of those ignore comments are places that were never type-safe previously.

closes #1282

shared/utils/parseDocumentSlug.ts

@@ -0,0 +1,15 @@
+export default function parseDocumentSlug(url: string) {
+  let parsed;
+
+  if (url[0] === "/") {
+    parsed = url;
+  } else {
+    try {
+      parsed = new URL(url).pathname;
+    } catch (err) {
+      return;
+    }
+  }
+
+  return parsed.replace(/^\/doc\//, "");
+}