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>

templates/base/head_script.tmpl

@@ -13,7 +13,6 @@ If you introduce mistakes in it, Gitea JavaScript code wouldn't run correctly.
 		assetUrlPrefix: '{{AssetUrlPrefix}}',
 		runModeIsProd: {{.RunModeIsProd}},
 		customEmojis: {{CustomEmojis}},
-		csrfToken: '{{.CsrfToken}}',
 		pageData: {{.PageData}},
 		notificationSettings: {{NotificationSettings}}, {{/*a map provided by NewFuncMap in helper.go*/}}
 		enableTimeTracking: {{EnableTimetracking}},