Move convert package to services (#22264)

Addition to #22256

The `convert` package relies heavily on different models which is
[disallowed by our definition of
modules](https://github.com/go-gitea/gitea/blob/main/CONTRIBUTING.md#design-guideline).
This helps to prevent possible import cycles.

Co-authored-by: Lunny Xiao <xiaolunwen@gmail.com>

services/convert/git_commit_test.go

@@ -0,0 +1,41 @@
+// Copyright 2020 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package convert
+
+import (
+	"testing"
+	"time"
+
+	repo_model "code.gitea.io/gitea/models/repo"
+	"code.gitea.io/gitea/models/unittest"
+	"code.gitea.io/gitea/modules/git"
+	api "code.gitea.io/gitea/modules/structs"
+	"code.gitea.io/gitea/modules/util"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestToCommitMeta(t *testing.T) {
+	assert.NoError(t, unittest.PrepareTestDatabase())
+	headRepo := unittest.AssertExistsAndLoadBean(t, &repo_model.Repository{ID: 1})
+	sha1, _ := git.NewIDFromString("0000000000000000000000000000000000000000")
+	signature := &git.Signature{Name: "Test Signature", Email: "test@email.com", When: time.Unix(0, 0)}
+	tag := &git.Tag{
+		Name:    "Test Tag",
+		ID:      sha1,
+		Object:  sha1,
+		Type:    "Test Type",
+		Tagger:  signature,
+		Message: "Test Message",
+	}
+
+	commitMeta := ToCommitMeta(headRepo, tag)
+
+	assert.NotNil(t, commitMeta)
+	assert.EqualValues(t, &api.CommitMeta{
+		SHA:     "0000000000000000000000000000000000000000",
+		URL:     util.URLJoin(headRepo.APIURL(), "git/commits", "0000000000000000000000000000000000000000"),
+		Created: time.Unix(0, 0),
+	}, commitMeta)
+}