[OSX] Fullscreen improvments

[michicc]

Fixes #8038

Motivation / Problem

The menu bar gets in the way in OSX fullscreen mode.
Also, quitting while in fullscreen mode looses the original window size, unlike e.g. under Windows.

Description

Hide Dock and menu bar in fullscreen mode and store the original windows size in the config, not the fullscreen size.

Checklist for review

Some things are not automated, and forgotten often. This list is a reminder for the reviewers.

• The bug fix is important enough to be backported? (label: 'backport requested')
• This PR affects the save game format? (label 'savegame upgrade')
• This PR affects the GS/AI API? (label 'needs review: Script API')
  • ai_changelog.hpp, gs_changelog.hpp need updating.
  • The compatibility wrappers (compat_*.nut) need updating.
• This PR affects the NewGRF API? (label 'needs review: NewGRF')
  • PR must be added to API tracker

[andythenorth]

Works as expected for me

• full screen has no menu bar
• full does not show dock
• behaviour is conventional for macOS when switching to/from OpenTTD in full screen mode
• window sizing is retained across restarts for variations of full screen / windowed
• tested for both ./openttd, and the bundle package built with cpack

macOS 10.15.7