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/user/settings/repos.tmpl

@@ -43,7 +43,6 @@
 														<p>{{ctx.Locale.Tr "repo.adopt_preexisting_content" $dir}}</p>
 													</div>
 													<form class="ui form" method="post" action="{{AppSubUrl}}/user/settings/repos/unadopted">
-														{{$.CsrfTokenHtml}}
 														<input type="hidden" name="id" value="{{$dir}}">
 														<input type="hidden" name="action" value="adopt">
 														{{template "base/modal_actions_confirm" $}}
@@ -60,7 +59,6 @@
 														<p>{{ctx.Locale.Tr "repo.delete_preexisting_content" $dir}}</p>
 													</div>
 													<form class="ui form" method="post" action="{{AppSubUrl}}/user/settings/repos/unadopted">
-														{{$.CsrfTokenHtml}}
 														<input type="hidden" name="id" value="{{$dir}}">
 														<input type="hidden" name="action" value="delete">
 														{{template "base/modal_actions_confirm" $}}