Make wxToolBar styles consistent and add wxTB_DEFAULT_STYLE.

Don't include wxBORDER_NONE in neither wxToolBar ctor and Create() nor
wxFrame::CreateToolBar() flags parameter, override GetDefaultBorder() in
wxToolBar itself instead to use the border style appropriate for the current
platform by default. This has the same effect -- the default border style is
used unless another one is explicitly specified -- but is more clear and
consistent.

Also add wxTB_DEFAULT_STYLE for consistency with the other classes.

Closes #15037.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@73757 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

include/wx/toolbar.h

@@ -60,7 +60,9 @@ enum
     wxTB_BOTTOM       = 0x2000,
 
     // lay out toolbar at the right edge of the window
-    wxTB_RIGHT        = 0x4000
+    wxTB_RIGHT        = 0x4000,
+
+    wxTB_DEFAULT_STYLE = wxTB_HORIZONTAL | wxTB_FLAT
 };
 
 #if wxUSE_TOOLBAR