Delegate the log string creation to wxLogFormatter. This allows defining a
custom object of a class derived from it to customize the log output instead
of having to override DoLogRecord() in wxLog itself.
Closes#13792.
git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@70086 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775