extension: Migrate to TypeScript 4.8

Per https://devblogs.microsoft.com/typescript/announcing-typescript-4-8/#unconstrained-generics-no-longer-assignable-to,
`Object.entries()` no longer accepts nullable objects.
The suggested fix is to add a `T extends {}` constraint, but that's
disallowed by https://typescript-eslint.io/rules/ban-types/. So instead
change the parameter types from `T` to `NonNull<T>`.

web/packages/extension/src/popup.ts

@@ -81,7 +81,7 @@ async function queryTabStatus(
     optionsChanged();
 }
 
-function objectsEqual<T>(x: T, y: T) {
+function objectsEqual<T>(x: NonNullable<T>, y: NonNullable<T>) {
     for (const [key, value] of Object.entries(x)) {
         if (y[key as keyof T] !== value) {
             return false;