expose DBus interface property names as symbols

Enable a way to access the property names of a given DBus interface as a
constexpr symbol via the header [1]

4 use-cases:

- printing error / debug logs with the property name.
  e.g. '${property} missing from configuration'

- accessing DBus properties in applications which do not yet use the PDI
  generated bindings.

- preventing typos in DBus property names

- estimating the impact of removing a given DBus property from an
  interface. When using these symbols, it would cause a build failure in
  applications relying on the existence of that property.

Tested: a newly added unit test is using this feature.

References:
[1] https://discordapp.com/channels/775381525260664832/867820390406422538/1423317550732673206

Change-Id: I7b2906b6b1b445c3a49868ff1d50ced6ccaa5336
Signed-off-by: Alexander Hansen <alexander.hansen@9elements.com>
diff --git a/test/meson.build b/test/meson.build
index f67bf32..de7c0e4 100644
--- a/test/meson.build
+++ b/test/meson.build
@@ -123,6 +123,7 @@
     'test_aserver_no_uninitialized_value_constructor',
     'test_aserver_emit_interfaces_added_signal',
     'test_aserver_multiple_interfaces',
+    'test_property_names',
 ]
 
 foreach t : uninit_tests
@@ -133,7 +134,7 @@
             f'gen/@t@.cpp',
             generated_sources,
             include_directories: [root_inc],
-            dependencies: [sdbusplus_dep, server_test_dep],
+            dependencies: [sdbusplus_dep, server_test_dep, gtest_dep],
         ),
     )
 endforeach