Refactor the setting to make unit test easier (#22405)

Some bugs caused by less unit tests in fundamental packages. This PR
refactor `setting` package so that create a unit test will be easier
than before.

- All `LoadFromXXX` files has been splited as two functions, one is
`InitProviderFromXXX` and `LoadCommonSettings`. The first functions will
only include the code to create or new a ini file. The second function
will load common settings.
- It also renames all functions in setting from `newXXXService` to
`loadXXXSetting` or `loadXXXFrom` to make the function name less
confusing.
- Move `XORMLog` to `SQLLog` because it's a better name for that.

Maybe we should finally move these `loadXXXSetting` into the `XXXInit`
function? Any idea?

---------

Co-authored-by: 6543 <6543@obermui.de>
Co-authored-by: delvh <dev.lh@web.de>

cmd/cmd.go

@@ -57,9 +57,10 @@ func confirm() (bool, error) {
 }
 
 func initDB(ctx context.Context) error {
-	setting.LoadFromExisting()
-	setting.InitDBConfig()
-	setting.NewXORMLogService(false)
+	setting.InitProviderFromExistingFile()
+	setting.LoadCommonSettings()
+	setting.LoadDBSetting()
+	setting.InitSQLLog(false)
 
 	if setting.Database.Type == "" {
 		log.Fatal(`Database settings are missing from the configuration file: %q.