This syncs the namespace declaration calls with element's events. A
test case is also added which enables threads of fastparser.

Change-Id: Ic40a380c8523688ee6b2ec76bb3d36a0452923bd
Reviewed-on: https://gerrit.libreoffice.org/27222Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Michael Meeks <michael.meeks@collabora.com>
Tested-by: Michael Meeks <michael.meeks@collabora.com>