Except for file callbacks, for these I have another change planned for
zero-copy import and it would be unwise to break stuff twice, providing
two sets of backwards compatibility wrappers. The image / scene
converter plugins went through a similar change earlier already and the
shader converters were made sane since the very beginning. OTOH audio
importers and text stuff are scheduled for merging with Trade or a
larger rework anyway, so I didn't see any point in updating those.
It's mostly a trivial change, except that returned String instances are
now also checked for non-default deleters same as Arrays because yes,
wow such flexibility compared to STL strings. Same was done for
ShaderTools::AbstractConverter already anyway, so nothing unheard-of
either.
The importer plugin interface version is bumped as this likely breaks
ABI in a nasty way that would lead to crashes.