videoencoder: pass upstream HDR information through output state
Don't copy HDR metadata from sink pad, because its caps may not have been set yet if GstVideoEncoder::negotiate is called from GstVideoEncoder::set_format, as e.g. vpx encoder does.
Don't copy HDR metadata from sink pad, because its caps may not have been set yet if GstVideoEncoder::negotiate is called from GstVideoEncoder::set_format, as e.g. vpx encoder does.