Update the button bezel to account for multi-line labels in wxOSX.

If a button was created using a normal single-line label (including empty one)
and then its label was changed to something multi-line later, its size stayed
wrong in wxOSX as it still used the fixed size bezel used by normal buttons.

Adjust the bezel after each bezel change now to update the size of the button
if necessary.

Closes #12491.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@72886 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

include/wx/osx/cocoa/private.h

@@ -270,7 +270,6 @@ public:
     void GetLayoutInset(int &left , int &top , int &right, int &bottom) const;
     void SetAcceleratorFromLabel(const wxString& label);
 
-private:
     NSButton *GetNSButton() const;
 };