move _TpBaseConnectionPrivate struct to its .c file

Fix https://bugs.freedesktop.org/show_bug.cgi?id=78377
add tp_intset_to_variant()

https://bugs.freedesktop.org/show_bug.cgi?id=77773
add tp_intset_from_variant()

https://bugs.freedesktop.org/show_bug.cgi?id=77773
handle-set: add GVariant API

Fix https://bugs.freedesktop.org/show_bug.cgi?id=77773
base-contact-list: use tp_handle_set_new_from_variant()
add tp_handles_are_valid_variant()

Will be needed to simply code in base-connection. Ideally the vfunc should
take a GVariant as well so we safe one conversion.
base-contact-list: use tp_handles_are_valid_variant()
base-contact-list: start using tp_handle_set_to_variant()

We are still using tp_handle_set_to_array() before calling
tp_base_connection_dup_contact_attributes(). Not sure if we should have a
version of this API taking a GVariant as well or not.
remove tp_handle_set_new_from_array()

It's no longer used by CMs and tp-glib.
stop using tp_handle_set_to_array() in tests
move tp_handle_set_to_array() as private API
contacts-conn: use the 'invisible' TpDBusPropertiesMixin API

https://bugs.freedesktop.org/show_bug.cgi?id=78376
simple-account-manager: use the 'invisible' TpDBusPropertiesMixin API

https://bugs.freedesktop.org/show_bug.cgi?id=78376
simple-account: use the 'invisible' TpDBusPropertiesMixin API

https://bugs.freedesktop.org/show_bug.cgi?id=78376
simple-channel-dispatch-operation: use the 'invisible' TpDBusPropertiesMixin API

https://bugs.freedesktop.org/show_bug.cgi?id=78376
simple-channel-dispatcher: use the 'invisible' TpDBusPropertiesMixin API

https://bugs.freedesktop.org/show_bug.cgi?id=78376
simple-channel-request: use the 'invisible' TpDBusPropertiesMixin API

https://bugs.freedesktop.org/show_bug.cgi?id=78376
textchann-group: use the 'invisible' TpDBusPropertiesMixin API

https://bugs.freedesktop.org/show_bug.cgi?id=78376
tls-certificate: use the 'invisible' TpDBusPropertiesMixin API

https://bugs.freedesktop.org/show_bug.cgi?id=78376
contactlist/conn: use the 'invisible' TpDBusPropertiesMixin API

https://bugs.freedesktop.org/show_bug.cgi?id=78376