slack: fix screen sharing on wayland

Slack blacklists the electron feature to allow screen capture via
Pipewire for unknown reasons. This change applies the same workaround
as the unofficial slack flatpack to get it working again.

(cherry picked from commit 5f6b9d7)

pkgs/applications/networking/instant-messengers/slack/default.nix

@@ -181,7 +181,11 @@ let
         --replace /usr/bin/ $out/bin/ \
         --replace /usr/share/pixmaps/slack.png slack \
         --replace bin/slack "bin/slack -s"
-
+    '' + lib.optionalString stdenv.hostPlatform.isLinux ''
+      # Prevent Un-blacklist pipewire integration to enable screen sharing on wayland.
+      # https://github.com/flathub/com.slack.Slack/issues/101#issuecomment-1807073763
+      sed -i -e 's/,"WebRTCPipeWireCapturer"/,"LebRTCPipeWireCapturer"/' $out/lib/slack/resources/app.asar
+    '' + ''
       runHook postInstall
     '';
   };