API: gst_value_array_append_and_take_value
API: gst_value_list_append_and_take_value

We were already using this internally, this makes it public for code
which frequently appends values which are expensive to copy (like
structures, arrays, caps, ...).

Avoids copies of the values for users. The passed GValue will also
be 0-memset'ed for re-use.

New users can replace this kind of code:
gst_value_*_append_value(mycontainer, &myvalue);
g_value_unset(&myvalue);

by:

gst_value_*_append_and_take_value(mycontainer, &myvalue);

https://bugzilla.gnome.org/show_bug.cgi?id=701632