tp_connection_manager_param_dup_variant_type: add

In order for this to work, TpProtocol now ignores parameters whose
D-Bus signatures are not a syntactically valid single complete type.

This is helpful for Mission Control to be able to migrate parameters
from untyped to typed storage - it stores parameters in terms of
GVariant.

Bug: https://bugs.freedesktop.org/show_bug.cgi?id=71093
Reviewed-by: Guillaume Desmottes <guillaume.desmottes@collabora.co.uk>
[added (transfer full) as requested in review -smcv]
TpProtocol: fix some suspicious memory management

It works fine as long as a preallocated GArray doesn't move its memory
buffer for no reason, but it's good to be obviously correct. Spotted while
working on the previous commit.

Bug: https://bugs.freedesktop.org/show_bug.cgi?id=71093
Reviewed-by: Guillaume Desmottes <guillaume.desmottes@collabora.co.uk>
0.23.1
maintainer-prepare-release: do "git tag" in srcdir
nano version