Use QLocale

When build the repo, here are a lot of deprecated messages, like:

‘Qt::DefaultLocaleShortDate’ is deprecated: Use QLocale
‘Qt::DefaultLocaleLongDate’ is deprecated: Use QLocale
‘Qt::SystemLocaleShortDate’ is deprecated: Use QLocale
‘Qt::SystemLocaleLongDate’ is deprecated: Use QLocale

These code need migration before Qt 6 breaks it.