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/gtk/toolbar.h

@@ -73,6 +73,9 @@ public:
     // --------------------------
 
 protected:
+    // choose the default border for this window
+    virtual wxBorder GetDefaultBorder() const { return wxBORDER_DEFAULT; }
+
     virtual wxSize DoGetBestSize() const;
     virtual GdkWindow *GTKGetWindow(wxArrayGdkWindows& windows) const;