Positioners: fix layout mirroring

Listen to positioner geometry changes when the _effective_ layout
direction is RTL.

Task-number: QTBUG-35095
Change-Id: If06955c6bb04e5bed2126b05489229278c192173
Reviewed-by: Jan Arve Sæther <jan-arve.saether@digia.com>
Flickable: fix crash in delayed press handling

Task-number: QTBUG-31328
Change-Id: Ic87e9b4db09242b49f104a8f38e4e420c62db75c
Reviewed-by: Robin Burchell <robin+qt@viroteck.net>
Reviewed-by: Martin Jones <martin.jones@jollamobile.com>