Refactor "route" related code, fix Safari cookie bug (#24330)

Fix #24176

Clean some misuses of route package, clean some legacy FIXMEs

---------

Co-authored-by: Giteabot <teabot@gitea.io>

modules/context/context_test.go

@@ -0,0 +1,40 @@
+// Copyright 2023 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package context
+
+import (
+	"net/http"
+	"testing"
+
+	"code.gitea.io/gitea/modules/setting"
+
+	"github.com/stretchr/testify/assert"
+)
+
+type mockResponseWriter struct {
+	header http.Header
+}
+
+func (m *mockResponseWriter) Header() http.Header {
+	return m.header
+}
+
+func (m *mockResponseWriter) Write(bytes []byte) (int, error) {
+	panic("implement me")
+}
+
+func (m *mockResponseWriter) WriteHeader(statusCode int) {
+	panic("implement me")
+}
+
+func TestRemoveSessionCookieHeader(t *testing.T) {
+	w := &mockResponseWriter{}
+	w.header = http.Header{}
+	w.header.Add("Set-Cookie", (&http.Cookie{Name: setting.SessionConfig.CookieName, Value: "foo"}).String())
+	w.header.Add("Set-Cookie", (&http.Cookie{Name: "other", Value: "bar"}).String())
+	assert.Len(t, w.Header().Values("Set-Cookie"), 2)
+	removeSessionCookieHeader(w)
+	assert.Len(t, w.Header().Values("Set-Cookie"), 1)
+	assert.Contains(t, "other=bar", w.Header().Get("Set-Cookie"))
+}