test: Add Object::invokeMethod() test

The test verifies correct behaviour of asynchronous method invocation
for Object instances.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Jacopo Mondi <jacopo@jmondi.org>
Reviewed-by: Niklas Söderlund <niklas.soderlund@ragnatech.se>

test/meson.build

@@ -24,6 +24,7 @@ public_tests = [
 internal_tests = [
     ['camera-sensor',                   'camera-sensor.cpp'],
     ['message',                         'message.cpp'],
+    ['object-invoke',                   'object-invoke.cpp'],
     ['signal-threads',                  'signal-threads.cpp'],
     ['threads',                         'threads.cpp'],
 ]