FileGDB: add a driver global mutex to protect all calls as the FileGDB API SDK is not thread-safe at all

git-svn-id: https://svn.osgeo.org/gdal/trunk@26323 f0d54148-0727-0410-94bb-9a71ac55c965
Additional commit related to r26323

git-svn-id: https://svn.osgeo.org/gdal/trunk@26324 f0d54148-0727-0410-94bb-9a71ac55c965
Merge branch 'trunk' into trunk_mingw