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

src/Package/Library/postgresql.php

@@ -98,7 +98,8 @@ class postgresql extends LibraryPackage
             . ' -Dextra_lib_dirs=' . escapeshellarg($lib_dir);
 
         // Build only the three frontend static libs (not the server) — keeps it fast and avoids
-        // needing every backend dependency. meson/ninja/win_bison/win_flex/perl come from PATH.
+        // needing every backend dependency. meson/ninja/win_bison/win_flex/perl come from the
+        // tool packages declared in the package config (tools@windows).
         $targets = 'src/interfaces/libpq/libpq.a src/common/libpgcommon.a src/port/libpgport.a';
 
         cmd()->cd($src)