Verify GPL compliance post-build

- access/libaccess_realrtsp_plugin.dll
- access/libdvdnav_plugin.dll
- access/libdvdread_plugin.dll
- access/libvnc_plugin.dll
- access/libdshow_plugin.dll
- audio_filter/libdolby_surround_decoder_plugin.dll
- audio_filter/libheadphone_channel_mixer_plugin.dll
- audio_filter/libmad_plugin.dll
- audio_filter/libmono_plugin.dll
- audio_filter/libsamplerate_plugin.dll
- codec/liba52_plugin.dll
- codec/libaribsub_plugin.dll
- codec/libdca_plugin.dll
- codec/libfaad_plugin.dll
- codec/liblibmpeg2_plugin.dll
- codec/libt140_plugin.dll
- codec/libx264_plugin.dll
- codec/libx265_plugin.dll
- control/*.dll
- demux/libmpc_plugin.dll
- demux/libreal_plugin.dll
- demux/libsid_plugin.dll
- gui/*.dll
- logger/libfile_logger_plugin.dll
- misc/libaudioscrobbler_plugin.dll
- misc/libexport_plugin.dll
- misc/liblogger_plugin.dll
- misc/libstats_plugin.dll
- misc/libvod_rtsp_plugin.dll
- packetizer/libpacketizer_a52_plugin.dll
- services_discovery/libmediadirs_plugin.dll
- services_discovery/libpodcast_plugin.dll
- services_discovery/libsap_plugin.dll
- stream_out/libstream_out_cycle_plugin.dll
- stream_out/libstream_out_rtp_plugin.dll
- video_filter/libpostproc_plugin.dll
- video_filter/librotate_plugin.dll

these packages need to be removed from future LibVLC.Windows releases and put into a new package LibVLC.Windows.GPL.

Edge cases to account for with the targets script:

• user adds old (pre-compliant) libvlc.windows package and new GPL package -> error.
• user adds GPL package only -> error

Documentation in this repo, libvlcsharp and nuget.org descriptions is needed.