macOS: Toga windows don't support close or minimize commands

[mhsmith]

Describe the bug

On macOS, Toga apps don't respond to Cmd-W for close or Cmd-M for minimize. They only respond to Cmd-Q for quit.

I also notice the app doesn’t have a Window menu, which is where those commands would normally appear.

Steps to reproduce

• On macOS, run briefcase dev in any app.
• When the window appears, press Cmd-W or Cmd-M.
• Computer gives an error sound, and nothing happens.

Expected behavior

Toga should support all standard window management commands on each OS.

Screenshots

Environment

• Operating System: macOS 12.6
• Python version: 3.11
• Software versions:
  • Briefcase: 0.3.11
  • Toga: 0.3.0dev39

Logs

No response

Additional context

No response