Allow using alignment with wxEXPAND and wxSHAPED in wxBoxSizer

Don't assert in wxBoxSizer when both alignment flags and wxEXPAND are
used together if wxSHAPED is also used, as such flag combinations may
make sense and so shouldn't be forbidden.

Add a unit test checking that this is allowed.

src/common/sizer.cpp

@@ -2071,7 +2071,10 @@ wxSizerItem *wxBoxSizer::DoInsert(size_t index, wxSizerItem *item)
             );
         }
 
-        if ( flags & wxEXPAND )
+        // Note that using alignment with wxEXPAND can make sense if wxSHAPED
+        // is also used, as the item doesn't necessarily fully expand in the
+        // other direction in this case.
+        if ( (flags & wxEXPAND) && !(flags & wxSHAPED) )
         {
             wxASSERT_MSG
             (
@@ -2097,7 +2100,7 @@ wxSizerItem *wxBoxSizer::DoInsert(size_t index, wxSizerItem *item)
             );
         }
 
-        if ( flags & wxEXPAND )
+        if ( (flags & wxEXPAND) && !(flags & wxSHAPED) )
         {
             wxASSERT_MSG(
                 !(flags & (wxALIGN_BOTTOM | wxALIGN_CENTRE_VERTICAL)),