Windows Qt6 builds based on vcpkg

[m-kuhn]

Description

Refs qgis/QGIS-Enhancement-Proposals#292
Continues #57414

This adds windows builds with Qt6, based on vcpkg dependencies.

The features WITH_BINDINGS, WITH_3D and WITH_GUI are supported and appropriately enable or disable building the required dependencies. Feature dependencies for server, opencl and quick are prepared but not yet wired.

Python support is consumed from https://github.com/open-vcpkg/python-registry/ . This is currently focused on shipping python dependencies that contain native code (dll's). Other dependencies can be installed using pip.

It is currently based on Qt 6.7.2

This also disables the mingw msys2 build, to reduce the CI infrastructure footprint. The other mingw builds which provide testable qt5 builds are still produced.

TODO:

• write README INSTALL.md

[github-actions]

🪟 Windows builds

Download Windows builds of this PR for testing.
Debug symbols for this build are available here.
(Built from commit 2c89431)

[nicogodet]

I tried the output build, I had to manually install numpy, urllib3, markupsafe and requests with pip to have a qgis without error at opening on a fresh profile.

I encounter some crashes (I tried to reproduce #53806 and it crashes when trying to set output path at opening expression dialog).

[m-kuhn]

Thank you @nicogodet

Regarding the python dependencies, I'm planning to come up with a follow up pull request to take care of these. I'm right now in the process of doing a mass update of python libs here open-vcpkg/python-registry#42

Regarding the crash, I'm not (yet) able to tell where this comes from. Qt6 support is still experimental and I think we'll want to keep these things in new issues which can be treated in the following months while stabilizing Qt6 support.

[nicogodet]

@m-kuhn crash reported here #59003

[m-kuhn]

I'll proceed and merge this and follow up with a pull request to improve the python situation

[MehdiChinoune]

I think cross-building on Fedora/mingw-w64 should be disabled instead of native building on MSYS2/mingw-w64.

[m-kuhn]

@MehdiChinoune no strong opinion on my side. I was just preserving the build that was published as pull request comments. Should we switch this to MSYS2/mingw-w64 (and if yes, what's better about it)?

[tsmcgrath]

@nicogodet See this comment for getting the freeze repro to run:
#53806 (comment)