Fix Mac OS X 10.9 build issue due to CGLContextObj return type.

[follower]

Prevents this compilation error on Mac OS X 10.9:

candidate function not viable: cannot convert argument of incomplete type 'void *' to
  'CGLContextObj' (aka '_CGLContextObject *')

The issue occurs because pre-Mac OS X 10.10 the CGLContextObj property had a return type of void * but in 10.10 it changed to a return type of struct _CGLContextObject *.

Also prevents a similar error with CGLPixelFormatObj property.

The issue appeared due to the recent addition of the call to CVDisplayLinkSetCurrentCGDisplayFromOpenGLContext() to work around a macOS 10.14 v-sync issue in b53f2d1.

Note:

• I've only tested this change by building on Mac OS X 10.9--I don't know if the addition of the static_cast will cause any issues on OS versions that don't require it.
• An alternative approach would be to use the implementation that appears to come from Apple-supplied examples (e.g. GLEssentials/GLEssentials/Source/Classes/OSX/GLEssentialsGLView.m) which would avoid the cast by explicitly storing the parameters into variables before making the function call:

CGLContextObj cglContext = [[self openGLContext] CGLContextObj];
CGLPixelFormatObj cglPixelFormat = [[self pixelFormat] CGLPixelFormatObj];
CVDisplayLinkSetCurrentCGDisplayFromOpenGLContext(displayLink, cglContext, cglPixelFormat);

Additional context

Initial CGLContextObj-related build error:

platform/osx/os_osx.mm:1582:2: error: no matching function for call to 'CVDisplayLinkSetCurrentCGDisplayFromOpenGLContext'
        CVDisplayLinkSetCurrentCGDisplayFromOpenGLContext(displayLink, context.CGLContextObj, pixelFormat.CGLPixelFormatObj);
        ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/Developer/SDKs/MacOSX10.9.sdk/System/Library/Frameworks/CoreVideo.framework/Headers/CVDisplayLink.h:100:20: note: candidate function not viable: cannot convert argument of incomplete type 'void *' to
      'CGLContextObj' (aka '_CGLContextObject *')
CV_EXPORT CVReturn CVDisplayLinkSetCurrentCGDisplayFromOpenGLContext(CVDisplayLinkRef displayLink, 

Subsequent CGLPixelFormatObj-related build error:

platform/osx/os_osx.mm:1582:2: error: no matching function for call to 'CVDisplayLinkSetCurrentCGDisplayFromOpenGLContext'
        CVDisplayLinkSetCurrentCGDisplayFromOpenGLContext(displayLink, static_cast<CGLContextObj>(context.CGLContextObj), pixelFormat.CGLPixelFormatObj);
        ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/Developer/SDKs/MacOSX10.9.sdk/System/Library/Frameworks/CoreVideo.framework/Headers/CVDisplayLink.h:100:20: note: candidate function not viable: cannot convert argument of incomplete type 'void *' to
      'CGLPixelFormatObj' (aka '_CGLPixelFormatObject *')
CV_EXPORT CVReturn CVDisplayLinkSetCurrentCGDisplayFromOpenGLContext(CVDisplayLinkRef displayLink, 
                   ^

Mac OS X 10.9 header with CGLContextObj property in NSOpenGL.h in AppKit framework: AppKit.framework/Versions/C/Headers/NSOpenGL.h

Mac OS X 10.10 header with CGLContextObj property in NSOpenGL.h in AppKit framework: AppKit.framework/Versions/C/Headers/NSOpenGL.h

Current Godot code:

godot/platform/osx/os_osx.mm

Line 1582 in 816341a

CVDisplayLinkSetCurrentCGDisplayFromOpenGLContext(displayLink, context.CGLContextObj, pixelFormat.CGLPixelFormatObj);

Mac OS X 10.9 header with CVDisplayLinkSetCurrentCGDisplayFromOpenGLContext() function in CVDisplayLink.h in CoreVideo framework: CoreVideo.framework/Versions/A/Headers/CVDisplayLink.h

Equivalent Mac OS X 10.11 (the version the declaration next changed) header with CVDisplayLinkSetCurrentCGDisplayFromOpenGLContext() function in CVDisplayLink.h in CoreVideo framework: CoreVideo.framework/Versions/A/Headers/CVDisplayLink.h

[bruvzg]

Removing this thing completely seems to be better idea: #33125

CVDisplayLink hack doesn't work properly on macOS 10.15, with it v-sync is stuck in permanently enabled state. CGLCPSwapInterval works as expected.

[follower]

Even if the DisplayLink hack is going to be removed at some point, FWIW I'd appreciate if this change--assuming it doesn't prevent compilation on later versions--could be merged for now so that I don't have to keep applying it locally.

[akien-mga]

If removing the CVDisplayLink workaround is the better solution, it would be good to do now for 3.2.
Otherwise I can indeed merge this PR as a stopgap solution until a refactoring. WDYT @bruvzg?

[bruvzg]

WDYT @bruvzg?

Better to remove it doesn't work on 10.15, and useless on previous versions: #33783

[akien-mga]

Superseded by #33783.