Provide execution context to QFuture continuations, instead of using
QMetaObject::invokeMethod calls for running in the main thread.
Change-Id: Ica7de19494065d677ffc94224781bfbe292b4f21
Reviewed-by: Leena Miettinen <riitta-leena.miettinen@qt.io>
Reviewed-by: Mårten Nordheim <marten.nordheim@qt.io>