DMG/HFS support

[JanisErdmanis]

This PR improves DMG bundling by enabling HFS+ images with full macOS metadata preservation. This better aligns with standard macOS application distribution practices, reduces the risk of notarization and compatibility issues, and enables deeper DMG customization than ISO-based images.

The build chain now follows the Mozilla recipe, roughly as follows:

# Stage the payload
rsync -a --copy-unsafe-links source/ stage/
chmod -R a+rX,a-st,u+w,go-w stage

# Create the HFS+ volume — using newfs_hfs
size=$(( $(du -s stage | cut -f1) / 1000 * 102 / 100 + 1 ))   # 2% slack
dd if=/dev/zero of=staged.hfs bs=1M count=$size
newfs_hfs -v "$volume_name" staged.hfs

# Populate and wrap — using hfsplus and dmg from libdmg_hfsplus_jll
hfsplus staged.hfs symlink "/ " /Applications   # Drag-to-Applications alias
hfsplus staged.hfs addall stage
dmg build staged.hfs out.dmg

Remaining work

• Add an HFS filesystem creation utility: [hfsprogs] new recipe v540.1.3 JuliaPackaging/Yggdrasil#14580
• Integrate the new HFS utility into the build chain
  • Test that hfsplus and the other utilities work together correctly when creating HFS+ images
  • Get the test suite running again
  • Replace du and dd with platform-independent implementations
  • Test hfsplus with the Jumbo Julia distribution to uncover any additional issues
• Clean up the implementation