QFileSystemEngine: make factory functions return unique_ptr<QABFE>

This makes the ownership of the returned pointer clearer. It also
matches reality, some call sites were already storing the pointer in a
unique_ptr.

Also shorten the function name to "createLegacyEngine", you have to read
its docs anyway to figure out what it does.

Drive-by changes: less magic numbers; use sliced(); return nullptr
instead of `0`.

Change-Id: I637759b4160b28b15adf5f6548de336887338dab
Reviewed-by: Qt CI Bot <qt_ci_bot@qt-project.org>
Reviewed-by: Assam Boudjelthia <assam.boudjelthia@qt.io>

0 files changed, 0 insertions, 0 deletions