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/wiki.go

@@ -0,0 +1,59 @@
+// Copyright 2021 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package convert
+
+import (
+	"time"
+
+	repo_model "code.gitea.io/gitea/models/repo"
+	"code.gitea.io/gitea/modules/git"
+	api "code.gitea.io/gitea/modules/structs"
+	"code.gitea.io/gitea/modules/util"
+	wiki_service "code.gitea.io/gitea/services/wiki"
+)
+
+// ToWikiCommit convert a git commit into a WikiCommit
+func ToWikiCommit(commit *git.Commit) *api.WikiCommit {
+	return &api.WikiCommit{
+		ID: commit.ID.String(),
+		Author: &api.CommitUser{
+			Identity: api.Identity{
+				Name:  commit.Author.Name,
+				Email: commit.Author.Email,
+			},
+			Date: commit.Author.When.UTC().Format(time.RFC3339),
+		},
+		Committer: &api.CommitUser{
+			Identity: api.Identity{
+				Name:  commit.Committer.Name,
+				Email: commit.Committer.Email,
+			},
+			Date: commit.Committer.When.UTC().Format(time.RFC3339),
+		},
+		Message: commit.CommitMessage,
+	}
+}
+
+// ToWikiCommitList convert a list of git commits into a WikiCommitList
+func ToWikiCommitList(commits []*git.Commit, total int64) *api.WikiCommitList {
+	result := make([]*api.WikiCommit, len(commits))
+	for i := range commits {
+		result[i] = ToWikiCommit(commits[i])
+	}
+	return &api.WikiCommitList{
+		WikiCommits: result,
+		Count:       total,
+	}
+}
+
+// ToWikiPageMetaData converts meta information to a WikiPageMetaData
+func ToWikiPageMetaData(title string, lastCommit *git.Commit, repo *repo_model.Repository) *api.WikiPageMetaData {
+	suburl := wiki_service.NameToSubURL(title)
+	return &api.WikiPageMetaData{
+		Title:      title,
+		HTMLURL:    util.URLJoin(repo.HTMLURL(), "wiki", suburl),
+		SubURL:     suburl,
+		LastCommit: ToWikiCommit(lastCommit),
+	}
+}