Context from https://github.com/bitcoin-core/gui/issues/578:
The most valued benefit will come when migrating to Qt 6, where QRegExp requires usage of an additional Core5Compat module.
Instead, all use cases of QRegExp could be ported to QRegularExpression.
qt , test: Add tests for searching in AddressBookPage dialog
qt: Use QRegularExpression in AddressBookSortFilterProxyModel class
Co-authored-by: João Barbosa <joao.paulo.barbosa@gmail.com>