Rationale:
- there was a lot of large objects passed by value, so potentially
there's a speed bump from this
- even for implicitly shared classes like QString/QList there's still
a (small) cost for copying the objects when there's no reason to
- it's the right thing to do!
events have not been defined in the sip file, therefore QgsFilterLineEdits
created in python did not receive the events, leading to visual glitches.
Fix#11372
