fix(postgresql): provision meson, ninja and winflexbison on windows

- 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

config/pkg/lib/postgresql.yml

@@ -17,6 +17,11 @@ postgresql:
   depends@windows:
     - openssl
     - zlib
+  tools@windows:
+    - meson
+    - ninja
+    - winflexbison
+    - strawberry-perl
   suggests@unix:
     - icu
     - libxslt