audio: Support loading of files from Qt embedded resources

Summary:
Library version has already been increased to 7.1.0 recently, and there
were no releases since then, so no need to increase it again.

Test Plan: tested with a modified version of KBlocks that loads sound files from its .qrc

Reviewers: #kde_games

Subscribers: jjorge, kde-games-devel, aacid

Differential Revision: https://phabricator.kde.org/D21678