qdoc expects a common installation directory for all examples in a
documentation project.
Fixes: QTBUG-120562
Change-Id: Iafcc3b1867e62179aabe991e6d4013dafaf61678
Reviewed-by: Tomi Korpipää <tomi.korpipaa@qt.io>
(cherry picked from commit 60542fd8ee)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>