test: Add test case for signal delivery across threads

The test case creates a receiver inheriting from Object, connects a
signal to one of its slot, moves the receiver to a different thread,
emits the signal and verifies that it gets delivered in the correct
thread with the expected value.

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

test/meson.build

@@ -22,6 +22,7 @@ public_tests = [
 internal_tests = [
     ['camera-sensor',                   'camera-sensor.cpp'],
     ['message',                         'message.cpp'],
+    ['signal-threads',                  'signal-threads.cpp'],
     ['threads',                         'threads.cpp'],
 ]