Add D-Bus introspection tests

Add D-Bus introspection tests

* lisp/net/dbus.el (dbus-annotation-deprecated): New defconst.

* test/lisp/net/dbus-tests.el  (dbus--tests-dir): New defvar.
(dbus--test-introspect, dbus--test-validate-interface)
(dbus--test-validate-annotations, dbus--test-validate-property)
(dbus--test-validate-m-or-s, dbus--test-validate-signal)
(dbus--test-validate-method): New defuns.
(dbus-test07-introspection): New test.

* test/lisp/net/dbus-resources/org.gnu.Emacs.TestDBus.xml:
New test data.