Linear color space support for opengl targets

related to #92 (closed)

Hello everyone! Working on that problem for about a month, can't figure out that's wrong, hope you will help

I have washed out colors from any sources on windows/android, basically testing with udp streaming of laptop screen using ffmpeg

Unity Project in linear colorspace Texture format RGBA64 after correction of RenderApiD3D11 based on previous issue, windows started to show up right colors

out->full_range     = false;

out->transfer       = m_linear ? libvlc_video_transfer_func_BT709 : libvlc_video_transfer_func_SRGB;

but after correction of RenderApi_OpenGLBase (where we can find the same parameters for libvlc_video_output_cfg_t) nothing changes

correction in RenderApi_OpenGLBase:

output->opengl_format = GL_RGBA;

output->full_range = false;

output->colorspace = libvlc_video_colorspace_BT709;

output->primaries  = libvlc_video_primaries_BT709;

output->transfer   = libvlc_video_transfer_func_BT709;

Related issue was about 2 years ago and no one telling any bad stuff about situation with colors at the moment, maybe I was wrong at some other point.

---> FIX to implement: #190 (comment 403093)