gstvalue: add internal _list_concat() that takes ownership of input values
gstvalue: add internal _list_concat() that takes ownership of input values

Avoids unnecessary copies.

shelsonjava/gstreamer,mparis/gstreamer,jpakkane/gstreamer,StreamUtils/gstreamer,StreamUtils/gstreamer,mparis/gstreamer,Lachann/gstreamer,jpxiong/gstreamer,krichter722/gstreamer,jpakkane/gstreamer,mparis/gstreamer,Lachann/gstreamer,jpakkane/gstreamer,centricular/gstreamer,krichter722/gstreamer,surround-io/gstreamer,mparis/gstreamer,surround-io/gstreamer,centricular/gstreamer,surround-io/gstreamer,jpxiong/gstreamer,surround-io/gstreamer,krichter722/gstreamer,Lachann/gstreamer,centricular/gstreamer,surround-io/gstreamer,jpakkane/gstreamer,StreamUtils/gstreamer,jpxiong/gstreamer,StreamUtils/gstreamer,shelsonjava/gstreamer,centricular/gstreamer,centricular/gstreamer,shelsonjava/gstreamer,shelsonjava/gstreamer,Lachann/gstreamer,jpxiong/gstreamer,StreamUtils/gstreamer,krichter722/gstreamer,krichter722/gstreamer,mparis/gstreamer,Lachann/gstreamer,jpakkane/gstreamer,shelsonjava/gstreamer,jpxiong/gstreamer