[Development] Proposal to raise the minimum CMake version needed to build and use Qt 6.12

[Alexandru Croitor]

Hi,

I'd like to propose raising the minimum required CMake version for building and using Qt 6.12 to CMake 3.25.

The previous minimum version was 3.22 (Qt 6.9+).

The last released version of CMake 3.25 is 3.25.3, released on Mar 8, 2023, which is 3+ years old now.

The rationale for the proposal:

- allow using newer features in public Qt CMake APIs (improved developer experience)
- ease maintenance (get rid of code paths that handle old cmake version bugs and behaviors)
- Qt 6.12 will be an LTS release. It will have to keep up with platforms updates and getting a newer platform to work with an older CMake version can be troublesome.

Why version 3.25? It's the highest version we can support given the constraints of the proposed Qt 6.12 development hosts.

The proposed development hosts for Qt 6.12: https://qt-project.atlassian.net/browse/QTBUG-145031
The cmake versions available on those hosts: https://qt-project.atlassian.net/browse/QTBUG-146221
The features we gain: https://qt-project.atlassian.net/browse/QTBUG-131169?focusedCommentId=2536151

Please reach out with any feedback or concerns.

Alexandru