CI: Add native Windows VS2019 build

CI: Add native Windows VS2019 build

Adds a native build of Mesa using Meson with the Visual Studio 2019
toolchain on a Windows host.

Though Docker is supported on Windows, Docker-in-Docker is not possible,
nor are podman and skopeo available. We handle this by creating the
container from a shell-executor Windows machine, which gives us a native
PowerShell that we can execute Docker from. This attempts to do the same
copy-from-upstream-or-create-if-not-exists optimisation as the
ci-templates do for our Linux builds, albeit open-coded in PowerShell.

The Mesa build itself is executed inside a container, using Meson and
Ninja.

Signed-off-by: Daniel Stone <daniels@collabora.com>
Reviewed-by: Eric Anholt <eric@anholt.net>
Acked-by: Jose Fonseca <jfonseca@vmware.com>
Acked-by: Brian Paul <brianp@vmware.com>
Acked-by: Eric Engestrom <eric@engestrom.ch>
Tested-by: Marge Bot <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/4304>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/4304>