Copy PlasmaCore binary qmldir file structure into bin for unit tests

This way tests pass before installation.

Test Plan:
Before patch

Created a broken env by unsetting QML2_IMPORT_PATH
Ran test. It failed

It passes.

Reviewers: Plasma, dfaure

Reviewed By: dfaure

Subscribers: kde-frameworks-devel

Tags: Frameworks

Differential Revision: https://phabricator.kde.org/D14743