This commit adds transitive dependencies to the plugins, so that a
sane set of default plugins get auto-imported when linking against a
module. It also provides a new function, qt5_import_plugins(), which
allows you to override the set of plugins that get imported. The decision
of whether or not to import a specific plugin is based on several custom
target properties and a very clever generator expression.
Note that this change only imports plugins on static Qt builds. It
does nothing on shared Qt builds, as the shared libraries already have
their own plugin import mechanism.
[ChangeLog][CMake] Added ability to auto-import non-qml plugins on
Reviewed-by: Simon Hausmann <email@example.com>