Export the locations of Qt5 packages on which modules depend

Qt5 packages provide libraries to VTK in the form of imported targets.
VTK libraries that link to them get exported with dependencies on the
imported targets.  We must make them available to applications that link
to these VTK libraries too.

Teach each module that depends on Qt5 to export code that runs when
an application loads the module as part of its build process.  Find
the needed Qt5 package on behalf of the application to satisfy the
module's dependency on it.

Change-Id: Ib638ccafa084fbb06c20eb09464265501ccafc80