Use a private undo manager for wxTextCtrl

This allows each control have its own undo history, independent of the
other ones, as expected by the wx API, rather than using an undo manager
shared by all controls in the same TLW.

include/wx/osx/cocoa/private.h

@@ -436,6 +436,8 @@ public:
     - (void)textDidChange:(NSNotification *)aNotification;
     - (void)changeColor:(id)sender;
 
+    @property (retain) NSUndoManager* undoManager;
+
     @end
 
     @interface wxNSComboBox : NSComboBox

src/osx/cocoa/textctrl.mm

@@ -426,6 +426,16 @@ NSView* wxMacEditHelper::ms_viewCurrentlyEdited = nil;
     }
 }
 
+- (instancetype)initWithFrame:(NSRect)frameRect
+{
+    self = [super initWithFrame:frameRect];
+    if ( self )
+    {
+        self.undoManager = [[[NSUndoManager alloc] init] autorelease];
+    }
+    return self;
+}
+
 - (void)textDidChange:(NSNotification *)aNotification
 {
     wxUnusedVar(aNotification);
@@ -434,6 +444,11 @@ NSView* wxMacEditHelper::ms_viewCurrentlyEdited = nil;
         impl->controlTextDidChange();
 }
 
+- (nullable NSUndoManager *)undoManagerForTextView:(NSTextView *)view
+{
+    return self.undoManager;
+}
+
 
 - (void)changeColor:(id)sender
 {
@@ -773,9 +788,7 @@ wxNSTextViewControl::wxNSTextViewControl( wxTextCtrl *wxPeer, WXWidget w, long s
 
     [tv setDelegate: tv];
 
-    m_undoManager = nil;
-    if ( wxPeer && wxPeer->GetParent() && wxPeer->GetParent()->GetPeer() && wxPeer->GetParent()->GetPeer()->GetWXWidget() )
-        m_undoManager = [wxPeer->GetParent()->GetPeer()->GetWXWidget() undoManager];
+    m_undoManager = tv.undoManager;
 
     [tv setAllowsUndo:YES];