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/api_repo_languages_test.go

@@ -28,7 +28,6 @@ func TestRepoLanguages(t *testing.T) {
 
 		// Save new file to master branch
 		req = NewRequestWithValues(t, "POST", "/user2/repo1/_new/master/", map[string]string{
-			"_csrf":         doc.GetCSRF(),
 			"last_commit":   lastCommit,
 			"tree_path":     "test.go",
 			"content":       "package main",