Qt3D: Don't chdir into a qrc data directory in QQmlDataTest

On Android the test data lives in resources, so the data
directory is ":/" and QDir::setCurrent() fails, aborting
initTestCase() for every test using this shared base.

Build a qrc URL for resource data directories and skip the
chdir when the scheme is qrc, matching qtdeclarative's
QQmlDataTest.

Pick-to: 6.12
Task-number: QTBUG-146930
Change-Id: Ifb4a3464107d640e3586b4706b4fd2d63ecc40d4
Reviewed-by: Ville Voutilainen <ville.voutilainen@qt.io>