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/repo/settings/branches.tmpl

@@ -13,7 +13,6 @@
 					{{ctx.Locale.Tr "repo.settings.default_branch_desc"}}
 				</p>
 				<form class="tw-flex" action="{{.Link}}" method="post">
-					{{.CsrfTokenHtml}}
 					<input type="hidden" name="action" value="default_branch">
 					<div class="ui dropdown selection search tw-flex-1 tw-mr-2 tw-max-w-96">
 						{{svg "octicon-triangle-down" 14 "dropdown icon"}}