Get rid of HB dependency in FT font engine

Instead of loading HB face in QFreetypeFace::getFace(), defer allocation
until the first FT font engine for that face gets initialized;
then, QFreetypeFace "reparents" and manages the loaded HB face.

Change-Id: I2ac8ead4c6ed25d341af9c9cf0c34dfb979f8390
Reviewed-by: Eskil Abrahamsen Blomfeldt <eskil.abrahamsen-blomfeldt@digia.com>
Add missing PLUGIN_CLASS_NAME

Change-Id: Ic2d59ac9194d6756c9f978fb1c13baf3fa7009b7
Reviewed-by: Miikka Heikkinen <miikka.heikkinen@digia.com>
Reviewed-by: Andy Shaw <andy.shaw@digia.com>
Extend QStyle API with a SH_Splitter_OpaqueResize styleHint

Currently the default for QSplitter::opaqueResize is hard coded,
which is less than ideal. Instead this should be provided as a
style hint via QStyle so as to give a more uniform look to all
applications.

Change-Id: I5711811f7b672e36aafcd292ed320308570a0390
Reviewed-by: Kevin Ottens <kevin.ottens@kdab.com>
Reviewed-by: Frederik Gladhorn <frederik.gladhorn@digia.com>
Reviewed-by: Olivier Goffart <ogoffart@woboq.com>