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/repo_fork_test.go

@@ -46,7 +46,6 @@ func testRepoFork(t *testing.T, session *TestSession, ownerName, repoName, forkO
 	_, exists = htmlDoc.doc.Find(fmt.Sprintf(".owner.dropdown .item[data-value=\"%d\"]", forkOwner.ID)).Attr("data-value")
 	assert.True(t, exists, "Fork owner '%s' is not present in select box", forkOwnerName)
 	req = NewRequestWithValues(t, "POST", link, map[string]string{
-		"_csrf":              htmlDoc.GetCSRF(),
 		"uid":                strconv.FormatInt(forkOwner.ID, 10),
 		"repo_name":          forkRepoName,
 		"fork_single_branch": forkBranch,