SIP update for QgsFilterLineEdit

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
Repack() shapefiles on unload whenever they have been modified

Previous preconditions that would only repack them when features have been
deleted seems to not have covered everything.

Fix #11007
Fix #10956 (QgsSnapper crash/freeze/issues)

QgsMapSettings instance of QgsMapCanvas may have been prematurely deleted by SIP.
The KeepReference annotation will force QgsMapCanvas wrapper to keep one more ref
to it, so its reference count will not go to zero while map canvas is still alive.