Refactor legacy unknwon/com package, improve golangci lint (#19284)

The main purpose is to refactor the legacy `unknwon/com` package.
1. Remove most imports of `unknwon/com`, only `util/legacy.go` imports the legacy `unknwon/com`
2. Use golangci's depguard to process denied packages
3. Fix some incorrect values in golangci.yml, eg, the version should be quoted string `"1.18"`
4. Use correctly escaped content for `go-import` and `go-source` meta tags
5. Refactor `com.Expand` to our stable (and the same fast) `vars.Expand`, our `vars.Expand` can still return partially rendered content even if the template is not good (eg: key mistach).

modules/util/legacy_test.go

@@ -0,0 +1,37 @@
+// Copyright 2022 The Gitea Authors. All rights reserved.
+// Use of this source code is governed by a MIT-style
+// license that can be found in the LICENSE file.
+
+package util
+
+import (
+	"crypto/aes"
+	"crypto/rand"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/unknwon/com" //nolint:depguard
+)
+
+func TestAESGCM(t *testing.T) {
+	t.Parallel()
+
+	key := make([]byte, aes.BlockSize)
+	_, err := rand.Read(key)
+	assert.NoError(t, err)
+
+	plaintext := []byte("this will be encrypted")
+
+	ciphertext, err := AESGCMEncrypt(key, plaintext)
+	assert.NoError(t, err)
+
+	decrypted, err := AESGCMDecrypt(key, ciphertext)
+	assert.NoError(t, err)
+
+	assert.Equal(t, plaintext, decrypted)
+
+	// at the moment, we make sure the result is the same as the legacy package, this assertion can be removed in next round refactoring
+	legacy, err := com.AESGCMDecrypt(key, ciphertext)
+	assert.NoError(t, err)
+	assert.Equal(t, legacy, plaintext)
+}