tp_group_mixin_get_members etc.: remove accessors for members

tp_group_mixin_get_local_pending_members_with_info() uses a dbus-glib
data type, and none of these are actually used in the five core CMs
(they all track members separately in any case).
Make them private if used in the implementation, or remove them entirely.

Bug: https://bugs.freedesktop.org/show_bug.cgi?id=77190
Reviewed-by: Xavier Claessens
tp_group_mixin_change_members: take a GVariant for the details

Bug: https://bugs.freedesktop.org/show_bug.cgi?id=77190
Reviewed-by: Xavier Claessens
Simplify TpPresenceMixin by removing all support for non-message parameters

Bug: https://bugs.freedesktop.org/show_bug.cgi?id=77191
Reviewed-by: Xavier Claessens
simple-conn: don't reimplement dbus-status

This used to be done so we could emulate a connection manager older
than telepathy-spec 0.19.2, but that functionality was removed in
commit 347307b7.

Bug: https://bugs.freedesktop.org/show_bug.cgi?id=77187
Reviewed-by: Xavier Claessens
TpBaseConnection: stop using tp_dbus_properties_mixin_getter_gobject_properties()

Using that tied us to having a GDBus property whose type matches the
dbus-glib type, which is API we don't want.

Bug: https://bugs.freedesktop.org/show_bug.cgi?id=77187
Reviewed-by: Xavier Claessens
TpBaseConnection:dbus-status, TpBaseConnection:requestable-channel-classes: remove

They are not used in Folks, Empathy, MC or the "big 5" CMs, except for one
use of dbus-status in helper code for Folks' regression tests (which will
disappear when resynced from telepathy-glib).

Bug: https://bugs.freedesktop.org/show_bug.cgi?id=77187
Reviewed-by: Xavier Claessens
TpExportableChannel: turn channel-properties into a GVariant

Bug: https://bugs.freedesktop.org/show_bug.cgi?id=77187
Reviewed-by: Xavier Claessens
TpBasePasswordChannel: stop most D-Bus properties from being GObject properties

may-save-response is still exposed as a GObject property, because it's
construct-only, so presumably there's some expectation that it would
be set at construct-time.

Bug: https://bugs.freedesktop.org/show_bug.cgi?id=77187
Reviewed-by: Xavier Claessens
Update gitignore