[Development] Maintainers, your action needed: Qt 5.12.3 changes files

[Jani Heikkinen]

Hi!

Initial ones here: https://codereview.qt-project.org/#/q/message:%22Add+changes+file+for+Qt+5.12.3%22,n,z

Please finalize those immediately and get approval.

br,
Jani Heikkinen
Release Manager