macOS signing improvements: allow signed app exporting as ZIP, sign DMG after exporting.
macOS signing improvements: allow signed app exporting as ZIP, sign DMG after exporting.

(cherry picked from commit 4bec713b8c1f714ca8d822057a76d86dc0c1ad13)

ex/godot,ex/godot,ex/godot,ex/godot,ex/godot,ex/godot,ex/godot,ex/godot