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/tool/winflexbison.yml

@@ -0,0 +1,12 @@
+winflexbison:
+  type: tool
+  artifact:
+    binary:
+      windows-x86_64: { type: url, url: 'https://github.com/lexxmark/winflexbison/releases/download/v2.5.25/win_flex_bison-2.5.25.zip', extract: '{pkg_root_path}/winflexbison' }
+  path@windows:
+    - '{pkg_root_path}\winflexbison'
+  tool:
+    provides:
+      - win_flex.exe
+      - win_bison.exe
+    binary-subdir: winflexbison