refactor!: move go-chi/session into Gitea (#39504)

The `gitea.com/go-chi/session` package only exists for Gitea, so it
moves into `modules/session` to fix its bugs directly. Fixes the flake
in
https://github.com/go-gitea/gitea/actions/runs/36726154500/job/109923538400.

- Sessions are only written back when changed, so a read-only request
can't revert a concurrent change or restore a logged-out session, like
https://github.com/go-macaron/session/commit/ae808a4a4660c802965c834299ab08f167effd12
- The session cookie is only set once a session holds data
- Every backend refreshes the expiry on load and file sessions are
written atomically
- Also fix  https://github.com/go-gitea/gitea/issues/36176

## ⚠️ BREAKING ⚠️

* the `mysql`, `postgres`, `couchbase` and `memcache` session providers
are removed, use `file`, `db` or `redis` instead
* login-related cookies are renamed to `gitea_session` and
`gitea_remember`, if you'd like to use the old names, set `COOKIE_NAME`
and `COOKIE_REMEMBER_NAME` in app.ini

---------

Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>

services/auth/source/oauth2/store.go

@@ -32,7 +32,6 @@ func (st *SessionsStore) New(r *http.Request, name string) (*sessions.Session, e
 	return st.getOrNew(r, name, true)
 }
 
-// getOrNew gets the session from the chi-session if it exists. Override permits the overriding of an unexpected object.
 func (st *SessionsStore) getOrNew(r *http.Request, name string, override bool) (*sessions.Session, error) {
 	store := session_module.GetContextSession(r)
 
@@ -55,7 +54,7 @@ func (st *SessionsStore) getOrNew(r *http.Request, name string, override bool) (
 	}
 
 	session.IsNew = override
-	session.ID = store.ID() // Simply copy the session id from the chi store
+	session.ID = store.ID()
 
 	return session, store.Set(name, session)
 }
@@ -65,7 +64,7 @@ func (st *SessionsStore) Save(r *http.Request, w http.ResponseWriter, session *s
 	store := session_module.GetContextSession(r)
 
 	if session.IsNew {
-		_, _ = session_module.RegenerateSession(w, r)
+		store.Regenerate(w, r)
 		session.IsNew = false
 	}