pulseaudio: reference wrapped binaries in service files

Since commit 3871f8be8d
("pulseaudioFull: fix wrapGApp wrapping"), the pulseaudio service files
have been referencing *unwrapped* binaries. This mostly hurts
pulseaudioFull, where using unwrapped binaries means there's no High
Fidelity A2DP profile at all. Plain pulseaudio (not -full) seems able to
use A2DP profile with SBC codec, but not aptX, as the latter requires
gstreamer / wrapper.

Since the wrapping of pulseaudio is a bit complicated (see referenced
commit), let's just fix the service files manually in preFixup.

Ref https://github.com/NixOS/nixpkgs/issues/203919.

pkgs/servers/pulseaudio/default.nix

@@ -165,6 +165,11 @@ stdenv.mkDerivation rec {
   + lib.optionalString (!libOnly) ''
     mkdir -p $out/bin
     ln -st $out/bin $out/.bin-unwrapped/*
+
+    # Ensure that service files use the wrapped binaries.
+    find "$out" -name "*.service" | while read f; do
+        substituteInPlace "$f" --replace "$out/.bin-unwrapped/" "$out/bin/"
+    done
   '';
 
   meta = {