Additions & fixes for lib copy, use only forwarded ptrs in LLAE interfaces.

Copy3rdPartyLibs needed to copy the now-corrected fmodexL libraries
and it had a bad library reference on Linux for release.  In
llaudio land, the audio engine interfaces, even the fmodex
specializations, seem to want to be external-structure free
so use a forward declaration and pointer to FMOD_DSP_DESCRIPTION
and deal with it in the ctor/dtor.