sal: remove OSL_ENSURE_FILE, better use SAL_LOG/SAL_INFO

Change-Id: I43d77cbf572acc4c27785990e28b43b35d71c96d
some notes about COM threading in LO generally and winaccessibility

- document general COM threading architecture in vcl README
- document winaccessiblitiy locking in README
- define _ATL_APARTMENT_THREADED for UAccCOM

Change-Id: I7c3fd952f2cdee7d245a818bf33c477e7ea20fc2