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

app/utils/pageVisibility.ts

@@ -0,0 +1,23 @@
+let hidden = "hidden";
+let visibilityChange = "visibilitychange";
+
+if ("hidden" in document) {
+  hidden = "hidden";
+  visibilityChange = "visibilitychange";
+} else if ("mozHidden" in document) {
+  // Firefox up to v17
+  hidden = "mozHidden";
+  visibilityChange = "mozvisibilitychange";
+} else if ("webkitHidden" in document) {
+  // Chrome up to v32, Android up to v4.4, Blackberry up to v10
+  hidden = "webkitHidden";
+  visibilityChange = "webkitvisibilitychange";
+}
+
+export function getVisibilityListener(): string {
+  return visibilityChange;
+}
+
+export function getPageVisible(): boolean {
+  return !document[hidden];
+}