QmlJS: Move the exported-C++-type detection out of C++ code.

It now lives in qmljstools/qmljsfindexportedcpptypes, all in one place.

Also ensures that the source code is available when a file is being
scanned for QML exports. This will enable checking comments for
annotations about the URI a plugin is usually imported as.

Change-Id: I1da36d0678e0a8d34b171dbe0f6b5690d89eb18b
Reviewed-on: http://codereview.qt.nokia.com/3392


Reviewed-by: Fawzi Mohamed <fawzi.mohamed@nokia.com>