Since commit 74407aef, tab pages|controls are
considered to be container widgets (thus, search for the nearest
non-layout parent will never find a tab page parent, breaking
rectangle control in many dialogs). I've no idea how many
other functions' behaviour this changes in an unexpected way,
so I've reverted that bit.

That however means implementing slightly different approach to
tdf#92630 in dialogs (for a tab dialog, find current tab page
and go through its children)

Change-Id: I3ff5ac13f04b1c5c799c7a1a3769108927809f31
Reviewed-on: https://gerrit.libreoffice.org/21615Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Thorsten Behrens <Thorsten.Behrens@CIB.de>