regression since 0157f0b1

my belief was that OK_Impl was only called in one
place, in sw/source/ui/fmtui/tmpdlg.cxx, so I
merged the use there into OK_Impl, but of course
there was another use in sfx2/source/dialog/tabdlg.cxx

Given that OK_Impl only called PrepareLeaveCurrentPage originally...

a) replace OK_Impl in sfx2/source/dialog/tabdlg.cxx
with PrepareLeaveCurrentPage, a no-op from the original state.
b) add an Apply method that does what I want, i.e.
call ok without closing the dialog, so we can retain
the fix of fdo#38606 to have "apply" immediately
apply the effect of pressing "ok" without closing
and reopening the dialog

Change-Id: I57e2e41c07ab9bf89ada98d1b9c3336db3493f19
(cherry picked from commit 8fd85527)
Reviewed-on: https://gerrit.libreoffice.org/1729Reviewed-by: Noel Power <noel.power@suse.com>
Tested-by: Noel Power <noel.power@suse.com>