Fix MacVim crashing on 10.9

This fixes MacVim to work again on OSX 10.9. It was previously crashing
on launch for last few versions.

titlebarAppearsTransparent call: This API was added in 10.10, and
previously MacVim wasn't properly guarding it with the proper OS version
check, causing it to crash under 10.9 (which is the lowest currently
supported macOS version).

CGContext call: The new stateful renderer is using a newer API to
retrieve the CGContext from the NS wrapper, but that was also only added
in 10.10. When compiling against older versions, just use the older,
now-deprecated API "graphicsPort" instead. It still works.

Also, change the version check for `safeAreaInsets` for non-native full
screen to use `@available` as well instead of checking for selector.
This is more consistent with how other code works and fixes a compiler
warning about not checking for OS version.

Fix #1212

Author: ychin

src/MacVim/MMCoreTextView.m

@@ -734,7 +734,12 @@ - (void)setNeedsDisplayFromRow:(int)row column:(int)col toRow:(int)row2
 - (void)drawRect:(NSRect)rect
 {
     NSGraphicsContext *context = [NSGraphicsContext currentContext];
+#if MAC_OS_X_VERSION_MIN_REQUIRED >= MAC_OS_X_VERSION_10_10
     CGContextRef ctx = context.CGContext;
+#else
+    CGContextRef ctx = [context graphicsPort];
+#endif
+
     [context setShouldAntialias:antialias];
     {
         CGColorSpaceRef colorSpace = CGColorSpaceCreateWithName(kCGColorSpaceSRGB);

src/MacVim/MMFullScreenWindow.m

@@ -382,7 +382,7 @@ - (NSEdgeInsets) viewOffset {
 
 #if (MAC_OS_X_VERSION_MAX_ALLOWED >= MAC_OS_VERSION_12_0)
     // Account for newer MacBook Pro's which have a notch, which can be queried using the safe area API.
-    if ([NSScreen instancesRespondToSelector:@selector(safeAreaInsets)]) {
+    if (@available(macos 12.0, *)) {
         const int safeAreaBehavior = [[NSUserDefaults standardUserDefaults]
                                       integerForKey:MMNonNativeFullScreenSafeAreaBehaviorKey];
 

src/MacVim/MMWindowController.m

@@ -571,8 +571,12 @@ - (void)refreshApperanceMode
     // has selected as a preference.
 
     // Transparent title bar setting
-    decoratedWindow.titlebarAppearsTransparent = [[NSUserDefaults standardUserDefaults]
-                                                  boolForKey:MMTitlebarAppearsTransparentKey];
+#if MAC_OS_X_VERSION_MAX_ALLOWED >= MAC_OS_X_VERSION_10_10
+    if (@available(macos 10.10, *)) {
+        decoratedWindow.titlebarAppearsTransparent = [[NSUserDefaults standardUserDefaults]
+                                                      boolForKey:MMTitlebarAppearsTransparentKey];
+    }
+#endif
 
     // No title bar setting
     if ([[NSUserDefaults standardUserDefaults]