QmlProfiler: Move the file finder into the QML model

This is the place where we need it most. In addition, this allows us to
use the DetailsRewriter's cache also on gotoSourceLocation.

Change-Id: I14e0f11ba7c8a2a3888b2e8439a375068b36e29a
Reviewed-by: Christian Kandeler <christian.kandeler@qt.io>
Reviewed-by: Ulf Hermann <ulf.hermann@qt.io>