lib: add a function to read the ABI version of the libvlc

For users of libvlc with manual DLL loading (especially languages not compatible with C that have to recode the access to the libvlc DLL) it is important to know the ABI version of the DLL, in case of API/ABI changes the wrapper need to be updated and know when the provided DLL package matches or not. This is especially critical for VLC 4.0 which has not changed version in 4 years and yet the libvlc API keeps changing.

This is similar to the versions of libavcodec/libavformat/etc. When the API is changed the version values should be updated as well, and hopefully documented as well.

This should also be backported to VLC 3.0.

Draft on top of !2883 (merged)