More or less:
find src -type f -exec sed -i "s/QtQuick.Layouts 1.3/QtQuick.Layouts 1.12/g" {} + && find src -type f -exec sed -i "s/import QtQuick 2.9/import QtQuick 2.12/g" {} + && find src -type f -exec sed -i "s/QtQuick.Particles 2.0/QtQuick.Particles 2.12/g" {} + && find src -type f -exec sed -i "s/QtQuick.Window 2.2/QtQuick.Window 2.12/g" {} + && find src -type f -exec sed -i "s/QtMultimedia 5.0/QtMultimedia 5.12/g" {} + && find src -type f -exec sed -i "s/QtQml 2.2/QtQml 2.12/g" {} + && find src -type f -exec sed -i "s/QtQml.Models 2.1/QtQml.Models 2.12/g" {} +