scylla-gdb.py: collection element func: accept references and pointers to collections
scylla-gdb.py: collection element func: accept references and pointers to collections

Add support to references (both lvalue and rvalue) and pointers to
collections as well, in addition to plain values.

Signed-off-by: Botond Dénes <a584fa4d75a0a85d721f44fb6e06315a2853b0b6@scylladb.com>
Message-Id: <20200624101305.428925-1-a584fa4d75a0a85d721f44fb6e06315a2853b0b6@scylladb.com>

scylladb/scylla,avikivity/scylla,scylladb/scylla,avikivity/scylla,scylladb/scylla,scylladb/scylla,avikivity/scylla