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/xss_test.go

@@ -21,7 +21,6 @@ func TestXSSUserFullName(t *testing.T) {
 
 	session := loginUser(t, user.Name)
 	req := NewRequestWithValues(t, "POST", "/user/settings", map[string]string{
-		"_csrf":     GetUserCSRFToken(t, session),
 		"name":      user.Name,
 		"full_name": fullName,
 		"email":     user.Email,