POC fix for Mac drawing bug

- Add a new selector setClipsToBounds
- Set this selector to true in Widget#drawRect
- See #1012

bundles/org.eclipse.swt/Eclipse SWT PI/cocoa/org/eclipse/swt/internal/cocoa/OS.java

@@ -1896,6 +1896,8 @@ public static Selector getSelector (long value) {
 public static final long sel_setShowsProgressPanel_ = Selector.sel_setShowsProgressPanel_.value;
 public static final long sel_setShowsResizeIndicator_ = Selector.sel_setShowsResizeIndicator_.value;
 public static final long sel_setShowsToolbarButton_ = Selector.sel_setShowsToolbarButton_.value;
+// See https://github.com/eclipse-platform/eclipse.platform.swt/issues/1012
+public static final long sel_setClipsToBounds_ = Selector.sel_setClipsToBounds_.value;
 public static final long sel_setSize_ = Selector.sel_setSize_.value;
 public static final long sel_setState_ = Selector.sel_setState_.value;
 public static final long sel_setString_ = Selector.sel_setString_.value;

bundles/org.eclipse.swt/Eclipse SWT PI/cocoa/org/eclipse/swt/internal/cocoa/Selector.java

@@ -1139,6 +1139,8 @@ public enum Selector {
 	, sel_setShowsProgressPanel_("setShowsProgressPanel:")
 	, sel_setShowsResizeIndicator_("setShowsResizeIndicator:")
 	, sel_setShowsToolbarButton_("setShowsToolbarButton:")
+	// See https://github.com/eclipse-platform/eclipse.platform.swt/issues/1012
+	, sel_setClipsToBounds_("setClipsToBounds:")
 	, sel_setSize_("setSize:")
 	, sel_setState_("setState:")
 	, sel_setString_("setString:")

bundles/org.eclipse.swt/Eclipse SWT/cocoa/org/eclipse/swt/widgets/Widget.java

@@ -759,6 +759,8 @@ void drawRect (long id, long sel, NSRect rect) {
 	if (!isDrawing()) return;
 	Display display = this.display;
 	NSView view = new NSView(id);
+	// See https://github.com/eclipse-platform/eclipse.platform.swt/issues/1012
+	OS.objc_msgSend(id, OS.sel_setClipsToBounds_, true);
 	display.isPainting.addObject(view);
 	NSGraphicsContext context = NSGraphicsContext.currentContext();
 	context.saveGraphicsState();