cocoa-cb: lock CGLContext on uninit and manual redraw

this fixes a crash on quit, when a CATransaction from a system owned
thread/event is happening at the same time. locking the context
synchronises these access and prevents the race condition.

the draw operation induced by any display call from the CAOpenGLLayer
doesn't need that lock, since the display function already does lock
that current context.

Fixes mpv-player#11681

video/out/cocoa_cb_common.swift

@@ -209,7 +209,9 @@ class CocoaCB: Common {
         uninit()
         uninitCommon()
 
+        layer?.lockCglContext()
         libmpv.deinitRender()
+        layer?.unlockCglContext()
         libmpv.deinitMPV(destroy)
     }
 

video/out/mac/gl_layer.swift

@@ -199,6 +199,14 @@ class GLLayer: CAOpenGLLayer {
         }
     }
 
+    func lockCglContext() {
+        CGLLockContext(cglContext)
+    }
+
+    func unlockCglContext() {
+        CGLUnlockContext(cglContext)
+    }
+
     override func copyCGLPixelFormat(forDisplayMask mask: UInt32) -> CGLPixelFormatObj {
         return cglPixelFormat
     }
@@ -219,10 +227,12 @@ class GLLayer: CAOpenGLLayer {
         super.display()
         CATransaction.flush()
         if isUpdate && needsFlip {
+            lockCglContext()
             CGLSetCurrentContext(cglContext)
             if libmpv.isRenderUpdateFrame() {
                 libmpv.drawRender(NSZeroSize, bufferDepth, cglContext, skip: true)
             }
+            unlockCglContext()
         }
         displayLock.unlock()
     }