test: Add tests for the Flags class

Add tests that exercise the whole API of the Flags class.

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

test/meson.build

@@ -40,6 +40,7 @@ internal_tests = [
     ['event-thread',                    'event-thread.cpp'],
     ['file',                            'file.cpp'],
     ['file-descriptor',                 'file-descriptor.cpp'],
+    ['flags',                           'flags.cpp'],
     ['hotplug-cameras',                 'hotplug-cameras.cpp'],
     ['mapped-buffer',                   'mapped-buffer.cpp'],
     ['message',                         'message.cpp'],