use pull model also for LOK text selection
Make LOK_CALLBACK_TEXT_SELECTION, LOK_CALLBACK_TEXT_SELECTION_START,
LOK_CALLBACK_TEXT_SELECTION_END and LOK_CALLBACK_TEXT_VIEW_SELECTION
also use pull model, i.e. LO core will only set a flag and when
CallbackFlushHandler needs the actual data it'll use getLOKPayload().
This again avoids a large number of messages passed to
CallbackFlushHandler only for them to be sooner or later discarded.
Change-Id: Ia7528039be996a6e9e8491b4eba3f4133582fa56
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/124146
Tested-by: Jenkins
Reviewed-by: Luboš Luňák <l.lunak@collabora.com>