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>

tests/integration/nonascii_branches_test.go

@@ -17,9 +17,7 @@ import (
 
 func setDefaultBranch(t *testing.T, session *TestSession, user, repo, branch string) {
 	location := path.Join("/", user, repo, "settings/branches")
-	csrf := GetUserCSRFToken(t, session)
 	req := NewRequestWithValues(t, "POST", location, map[string]string{
-		"_csrf":  csrf,
 		"action": "default_branch",
 		"branch": branch,
 	})