Replace CSRF cookie with CrossOriginProtection (#36183)

Removes the CSRF cookie in favor of
[`CrossOriginProtection`](https://pkg.go.dev/net/http#CrossOriginProtection)
which relies purely on HTTP headers.

Fixes: https://github.com/go-gitea/gitea/issues/11188
Fixes: https://github.com/go-gitea/gitea/issues/30333
Helps: https://github.com/go-gitea/gitea/issues/35107

TODOs:

- [x] Fix tests
- [ ] Ideally add tests to validates the protection

---------

Signed-off-by: wxiaoguang <wxiaoguang@gmail.com>
Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>

web_src/js/features/pull-view-file.ts

@@ -28,7 +28,7 @@ export function initViewedCheckboxListenerFor() {
     // To prevent double addition of listeners
     form.setAttribute('data-has-viewed-checkbox-listener', String(true));
 
-    // The checkbox consists of a div containing the real checkbox with its label and the CSRF token,
+    // The checkbox consists of a div containing the real checkbox with its label,
     // hence the actual checkbox first has to be found
     const checkbox = form.querySelector<HTMLInputElement>('input[type=checkbox]')!;
     checkbox.addEventListener('input', function() {