Add wxToolBarTool::Get{Normal,Disabled}BitmapBundle() accessors

The existing variants returning wxBitmap are insufficient for non-MSW
ports where the toolbar bitmap size is unavailable otherwise, as
GetToolBitmapSize() value doesn't really correspond to it (which is a
problem on its own, but there is not much that can be done about it by
now).

Having these functions allows to retrieve the actually used bitmap size
by using wxBitmapBundle::GetDefaultSize().

include/wx/tbarbase.h

@@ -146,6 +146,9 @@ public:
         { return m_kind == wxITEM_CHECK || m_kind == wxITEM_RADIO; }
 
     // attributes
+    wxBitmapBundle GetNormalBitmapBundle() const { return m_bmpNormal; }
+    wxBitmapBundle GetDisabledBitmapBundle() const { return m_bmpDisabled; }
+
     wxBitmap GetNormalBitmap(const wxSize& size = wxDefaultSize) const
         { return m_bmpNormal.GetBitmap(size); }
     wxBitmap GetDisabledBitmap(const wxSize& size = wxDefaultSize) const

interface/wx/toolbar.h

@@ -112,6 +112,26 @@ public:
     bool IsToggled() const;
     bool CanBeToggled() const;
 
+    /**
+        Return the bundle containing normal tool bitmaps.
+
+        This bundle may be invalid if the tool doesn't show a bitmap.
+
+        @since 3.1.6
+     */
+    wxBitmapBundle GetNormalBitmapBundle() const;
+
+    /**
+        Return the bundle containing disabled tool bitmaps.
+
+        This bundle may be invalid if the tool doesn't show a bitmap or doesn't
+        have a specific disabled bitmap creates one automatically from the
+        normal bitmap.
+
+        @since 3.1.6
+     */
+    wxBitmapBundle GetDisabledBitmapBundle() const;
+
     wxBitmap GetNormalBitmap() const;
     wxBitmap GetDisabledBitmap() const;