- add a python-win tool package that unzips the official python.org
nuget package into the pkgroot (venv and ensurepip included)
- meson uses it to build its venv and only falls back to a system
python, so no manual environment setup is needed
- the meson build assumed meson/ninja/win_flex/win_bison/perl on PATH,
which only held on machines that had them installed
- add meson, ninja and winflexbison tool packages and declare them via
tools@windows on postgresql, together with the existing strawberry-perl
- meson no longer ships a Windows MSI, so the wheel is installed offline
into a venv: postgres re-invokes meson through find_program, which
needs the real meson.exe launcher pip generates
