Remove legacy unknwon/com package (#19298)

Follows: #19284
* The `CopyDir` is only used inside test code
* Rewrite `ToSnakeCase` with more test cases
* The `RedisCacher` only put strings into cache, here we use internal `toStr` to replace the legacy `ToStr`
* The `UniqueQueue` can use string as ID directly, no need to call `ToStr`

contrib/pr/checkout.go

@@ -112,7 +112,7 @@ func runPR() {
 	unittest.LoadFixtures()
 	util.RemoveAll(setting.RepoRootPath)
 	util.RemoveAll(models.LocalCopyPath())
-	util.CopyDir(path.Join(curDir, "integrations/gitea-repositories-meta"), setting.RepoRootPath)
+	unittest.CopyDir(path.Join(curDir, "integrations/gitea-repositories-meta"), setting.RepoRootPath)
 
 	log.Printf("[PR] Setting up router\n")
 	// routers.GlobalInit()