zbus_macros: add property(emits_changed_signal="...") attribute
This adds macros support for the standard annotation
org.freedesktop.DBus.Property.EmitsChangedSignal
, see
https://dbus.freedesktop.org/doc/dbus-specification.html#introspection-format.
The four well-known values (true, false, const, invalidates)
can now be used through a new macro attribute, e.g.
#[dbus_proxy(property(emits_changed_signal = "false")
.
Closes: #253 (closed)