frontend: Upgrade TypeScript from 2.9.2 to 4.4.2 (#387)

* Upgrade TS from 2.9.2 to 4.4.2

* Avoid mutating a readonly array

`list` is a readonly array but `sort` will mutate the array in-place.
In newer version of TS, it can catch this unexpected behavior.

To avoid mutating a readonly array, we can sort with a new array with
either `[...list]` or `list.slice()`.

* Fix arguments of `window.location.reload`

The `reload` function type definition in `lib.dom.d.ts` takes 0
arguments now. So, we cannot pass a boolean to it.

Also, based on the documentation on MDN, Firefox is the only browser who
supports passing a `forceForget` boolean to `reload` function.
So, I wonder it should be fine to remove the boolean argument and align
the behavior to other browsers.

Ref: https://developer.mozilla.org/en-US/docs/Web/API/Location/reload

frontend/src/common/helpers.ts

@@ -119,7 +119,9 @@ export class NumStats<T extends number> {
 
     let sum = 0;
 
-    for (const n of list.sort((a, b) => a - b).slice(extremes, -extremes)) {
+    for (const n of [...list]
+      .sort((a, b) => a - b)
+      .slice(extremes, -extremes)) {
       sum += n;
     }