Cocoa: Replace global autorelease pool with blocks

This is another small step towards having GLFW play nice with other
toolkits sharing the same process, including AppKit.

Any macOS platform function that touches Cocoa must now wrap itself in
an autoreleasepool block.

Since GLFW no longer provides an autoreleasepool outside of its
functions, THIS MAY BREAK EXISTING CODE MIXING GLFW AND COCOA.  Sorry!
Please add your own autoreleasepool blocks as needed.

Fixes #1107.
Closes #1114.

src/cocoa_monitor.m

@@ -387,17 +387,23 @@ void _glfwPlatformFreeMonitor(_GLFWmonitor* monitor)
 
 void _glfwPlatformGetMonitorPos(_GLFWmonitor* monitor, int* xpos, int* ypos)
 {
+    @autoreleasepool {
+
     const CGRect bounds = CGDisplayBounds(monitor->ns.displayID);
 
     if (xpos)
         *xpos = (int) bounds.origin.x;
     if (ypos)
         *ypos = (int) bounds.origin.y;
+
+    } // autoreleasepool
 }
 
 void _glfwPlatformGetMonitorContentScale(_GLFWmonitor* monitor,
                                          float* xscale, float* yscale)
 {
+    @autoreleasepool {
+
     if (!refreshMonitorScreen(monitor))
         return;
 
@@ -408,12 +414,16 @@ void _glfwPlatformGetMonitorContentScale(_GLFWmonitor* monitor,
         *xscale = (float) (pixels.size.width / points.size.width);
     if (yscale)
         *yscale = (float) (pixels.size.height / points.size.height);
+
+    } // autoreleasepool
 }
 
 void _glfwPlatformGetMonitorWorkarea(_GLFWmonitor* monitor,
                                      int* xpos, int* ypos,
                                      int* width, int* height)
 {
+    @autoreleasepool {
+
     if (!refreshMonitorScreen(monitor))
         return;
 
@@ -427,10 +437,14 @@ void _glfwPlatformGetMonitorWorkarea(_GLFWmonitor* monitor,
         *width = frameRect.size.width;
     if (height)
         *height = frameRect.size.height;
+
+    } // autoreleasepool
 }
 
 GLFWvidmode* _glfwPlatformGetVideoModes(_GLFWmonitor* monitor, int* count)
 {
+    @autoreleasepool {
+
     CFArrayRef modes;
     CFIndex found, i, j;
     GLFWvidmode* result;
@@ -469,10 +483,14 @@ GLFWvidmode* _glfwPlatformGetVideoModes(_GLFWmonitor* monitor, int* count)
     CFRelease(modes);
     CVDisplayLinkRelease(link);
     return result;
+
+    } // autoreleasepool
 }
 
 void _glfwPlatformGetVideoMode(_GLFWmonitor* monitor, GLFWvidmode *mode)
 {
+    @autoreleasepool {
+
     CGDisplayModeRef displayMode;
     CVDisplayLinkRef link;
 
@@ -483,10 +501,14 @@ void _glfwPlatformGetVideoMode(_GLFWmonitor* monitor, GLFWvidmode *mode)
     CGDisplayModeRelease(displayMode);
 
     CVDisplayLinkRelease(link);
+
+    } // autoreleasepool
 }
 
 GLFWbool _glfwPlatformGetGammaRamp(_GLFWmonitor* monitor, GLFWgammaramp* ramp)
 {
+    @autoreleasepool {
+
     uint32_t i, size = CGDisplayGammaTableCapacity(monitor->ns.displayID);
     CGGammaValue* values = calloc(size * 3, sizeof(CGGammaValue));
 
@@ -508,10 +530,14 @@ GLFWbool _glfwPlatformGetGammaRamp(_GLFWmonitor* monitor, GLFWgammaramp* ramp)
 
     free(values);
     return GLFW_TRUE;
+
+    } // autoreleasepool
 }
 
 void _glfwPlatformSetGammaRamp(_GLFWmonitor* monitor, const GLFWgammaramp* ramp)
 {
+    @autoreleasepool {
+
     int i;
     CGGammaValue* values = calloc(ramp->size * 3, sizeof(CGGammaValue));
 
@@ -529,6 +555,8 @@ void _glfwPlatformSetGammaRamp(_GLFWmonitor* monitor, const GLFWgammaramp* ramp)
                                 values + ramp->size * 2);
 
     free(values);
+
+    } // autoreleasepool
 }