editeng: fix more 32-bit Time breakage

SfxDateTimeItem and SvxExtTimeField need to use 64-bit integer to store
Time as well.  These classes also have binary serialization
Load()/Save() methods but they are unlikely to be used in a persistent
way, just for the clipboard.

The problem is easy to reproduce in Impress: Insert->Field->Time(fixed)

(regression from 9830fd36dbdb72c79703b0c61efc027fba793c5a)

Change-Id: I5946c5b94dd5a509805b6dc40461bbd910caffc4
(cherry picked from commit 7b9c61c7f20a679c5316a288c2ec2ffbf04b4200)
Reviewed-on: https://gerrit.libreoffice.org/7021
Reviewed-by: Caolán McNamara <caolanm@redhat.com>
Tested-by: Caolán McNamara <caolanm@redhat.com>