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/branch/list.tmpl

@@ -230,7 +230,6 @@
 
 	<form class="ui form" id="create-branch-form" action="" data-base-action="{{.Link}}/_new/branch/" method="post">
 		<div class="content">
-			{{.CsrfTokenHtml}}
 			<div class="field">
 				{{ctx.Locale.Tr "repo.branch.create_new_branch"}}
 				<span id="modal-create-branch-from-span"></span>
@@ -250,7 +249,6 @@
 	</div>
 	<form class="ui form" action="{{$.Repository.Link}}/branches/rename" method="post">
 		<div class="content">
-			{{.CsrfTokenHtml}}
 			<div class="field default-branch-warning">
 				<span class="text red">{{ctx.Locale.Tr "repo.branch.warning_rename_default_branch"}}</span>
 			</div>