Relevant part of the PR description
> During shutdown QApplication exits the main event loop, then re-enter again.
>
> This PR streamlines shutdown process by removing the need to interrupt the main event loop.
> qt, refactor: Allocate SendConfirmationDialog instances on heap
>
> This change is require for the next commit.
https://github.com/bitcoin-core/gui/pull/336/commits/b4e0d2c43181ad97c15b252e95181e2c3f6c1d2a
> qt: Do not exit and re-enter main event loop during shutdown
https://github.com/bitcoin-core/gui/pull/336/commits/f3a17bbe5f7d23b6ecc20e363920492b50859dad
> qt, refactor: Drop intermediate BitcoinApplication::shutdownResult slot
https://github.com/bitcoin-core/gui/pull/336/commits/451ca244db8bc71ffc3cc9982d025f144cc8f3bc
For me this backport is mainly about grabbing the refactorings that makes core-gui#586 (Qt 6 readiness) more straightforward to backport
This concludes backport of core-gui#336
Depends on D18149