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/auth/grant.tmpl

@@ -19,7 +19,6 @@
 		</div>
 		<div class="ui attached segment tw-text-center">
 			<form method="post" action="{{AppSubUrl}}/login/oauth/grant">
-				{{.CsrfTokenHtml}}
 				<input type="hidden" name="client_id" value="{{.Application.ClientID}}">
 				<input type="hidden" name="state" value="{{.State}}">
 				<input type="hidden" name="scope" value="{{.Scope}}">