Combine two macOS installers into one universal binary

[jclarkeSTFC]

Describe the outcome that is desired.

Currently we have a DMG installer for x86_64, and one for ARM, but I think we can combine these into one universal DMG with both architectures included.

Describe any solutions you are considering

Here's what Copilot had to say for itself:

#!/bin/bash

set -e

# Input DMG paths
DMG_X86="$1"
DMG_ARM="$2"
APP_NAME="YourApp.app"
BINARY_NAME="YourApp"

# Mount DMGs
echo "Mounting DMGs..."
MOUNT_X86=$(hdiutil attach "$DMG_X86" | grep Volumes | awk '{print $3}')
MOUNT_ARM=$(hdiutil attach "$DMG_ARM" | grep Volumes | awk '{print $3}')

# Extract binaries
echo "Extracting binaries..."
cp "$MOUNT_X86/$APP_NAME/Contents/MacOS/$BINARY_NAME" ./binary_x86_64
cp "$MOUNT_ARM/$APP_NAME/Contents/MacOS/$BINARY_NAME" ./binary_arm64

# Create universal binary
echo "Creating universal binary..."
lipo -create -output "$BINARY_NAME"_universal binary_x86_64 binary_arm64

# Copy one of the app bundles to modify
echo "Preparing app bundle..."
cp -R "$MOUNT_ARM/$APP_NAME" "./$APP_NAME"
cp "$BINARY_NAME"_universal "./$APP_NAME/Contents/MacOS/$BINARY_NAME"

# Unmount DMGs
echo "Unmounting DMGs..."
hdiutil detach "$MOUNT_X86"
hdiutil detach "$MOUNT_ARM"

# Create new DMG
echo "Creating new DMG..."
hdiutil create -volname "$APP_NAME" -srcfolder "./$APP_NAME" -ov -format UDZO "${APP_NAME%.app}_Universal.dmg"

echo "✅ Universal DMG created: ${APP_NAME%.app}_Universal.dmg"

Additional context

See #38990

[thomashampson]

Not sure if we want to do this, won;t it double the size of the package that people need to donwload?