Rework `ScriptThread::handle_input_event` for correct behaviour and
better performance
1. Only trigger click event with primary button, according to spec
2. Avoid unnecessary clone of `ConstellationInputEvent`
This is a follow up of #36413
Testing: Manually tested. Right mouse won't trigger click event now.
Fixes: #35666
cc @jdm @xiaochengh
Signed-off-by: Euclid Ye <yezhizhenjiakang@gmail.com>