mlang/tests: Use BSTR strings instead of plain WCHARs when API tells so

[Dmitry Timoshkov]

Nikolay Sivov <nsivov at codeweavers.com> wrote:

> > The tests were written this way to ensure that mlang methods do not depend
> > on BSTR layout (and yes, at least IE6 depends on this).
> >
> 
> If IE6 abuses it in this way it should have been a separate test with 
> explicit comment.

There is no point in adding a separate test if all tested mlang methods
behave that way.

-- 
Dmitry.