Change EnableNoYieldMode(bool) to better names

It makes no sense to disable something via an Enable function.
I have split the function into Enable and Disable functions, and
update the code accordingly.

Conflicts:
	include/vcl/svapp.hxx

Change-Id: Ic05d69796f43e802a4a2a16aaca44433b6eaa018
Reviewed-on: https://gerrit.libreoffice.org/7525
Reviewed-by: Caolán McNamara <caolanm@redhat.com>
Tested-by: Caolán McNamara <caolanm@redhat.com>