This patch aims to implement the session management available on macOS.
Currently applicationShouldTerminate is just a go through that closes
everything and ends the application. The new implementation calls
first appCommitData and cancels the termination properly if required.
This means that if a user wishes to logout, Qt applications can now
cancel that like e.g. answering to Safari asking whether it is ok to
close because of a number of opened tab/window.
Fixes: QTBUG-33034
Change-Id: Id5d7416cb74c762c5424a77c9c7664f0749da7f6
Reviewed-by: Tor Arne Vestbø <tor.arne.vestbo@qt.io>
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