[[ Bug 12686 ]] Make sure file dialogs attempt to sheet against the defaultStack before the topStack.
Merge branch 'bugfix-12686' into release-6.6.3
Merge remote-tracking branch 'origin/bugfix-12686' into bugfix-12686_platform

Conflicts:
	engine/src/osxans.mm
[[ Bug 12686 ]] Previous change ported to platform API.
Merge branch 'bugfix-12686_platform' into develop
Merge branch 'release-6.6.3' into develop