[macOS] Add ability to open multiple editor instances and global/dock menu access

[bruvzg]

Adds methods to access macOS dock and global menu.

Adds "New Windows" dock menu item (editor and project manager).
Adds favourite/recent project list to project manager dock menu.
Adds opened scene list to editor dock menu.

Double-clicking ".godot" files in Finder now open new instance as well.

[bruvzg]

Nice, clang-format is suggesting change that's causing build to fail on macOS.

[akien-mga]

Nice, clang-format is suggesting change that's causing build to fail on macOS.

Hm, that's bad. The space in > > is needed in C++03, but we won't need it anymore when we move to C++11. The .clang-format file defines Standard: Cpp03, so it handles it properly in C++ files, but it seems like the ObjC++ files follow a different standard.

[akien-mga]

4912f57 should fix the clang-format issue.

[samgreen]

I don't have much to add other than a 👍 on this. Would be a big quality of life improvement for those of us building games on OS X.

[akien-mga]

The macOS-specific changes seem good to me.

CC @reduz and @hpvb to review the added OS APIs though, I wonder if it's fine to add those if they're only used on one platform.

[akien-mga]

I wonder if it's fine to add those if they're only used on one platform.

This is still my main concern with this PR, I don't want the OS singleton to get too many OS-specific features.

Would it be possible to implement this feature ad hoc in the macOS platform, exposing the relevant configuration in the platform's export settings? I see that the global menu action should be defined from script, so I guess this wouldn't play well with export options :/

[akien-mga]

Thanks!