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>

contrib/pr/checkout.go

@@ -49,7 +49,8 @@ func runPR() {
 		log.Fatal(err)
 	}
 	setting.SetCustomPathAndConf("", "", "")
-	setting.LoadAllowEmpty()
+	setting.InitProviderAllowEmpty()
+	setting.LoadCommonSettings()
 
 	setting.RepoRootPath, err = os.MkdirTemp(os.TempDir(), "repos")
 	if err != nil {
@@ -82,7 +83,7 @@ func runPR() {
 		setting.Database.Path = ":memory:"
 		setting.Database.Timeout = 500
 	*/
-	dbCfg := setting.Cfg.Section("database")
+	dbCfg := setting.CfgProvider.Section("database")
 	dbCfg.NewKey("DB_TYPE", "sqlite3")
 	dbCfg.NewKey("PATH", ":memory:")