Always use active wxTranslations instance via wxLocale.

Always use active wxTranslations instance via wxLocale.

Don't use m_translations directly, if the user made changes to
wxTranslations instance, it would be too confusing if calls through
wxLocale compat API did nothing.

Also don't change active wxTranslations object from wxLocale if already
done by user, only call wxTranslations::Set() from wxLocale constructor
if it wasn't already set by the user. Still do if wxTranslations
instance currently in use was set by previous wxLocale on the locale
stack.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@64165 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775