Allow changing horizontal alignment of numeric cells in wxGrid.

wxGridCellAttr didn't provide any way to query its alignment attributes
without falling back to the (always defined) default alignment so the code in
wxGridCellNumberRenderer and similar classes simply always used right
alignment,

Add a new wxGridCellAttr::GetNonDefaultAlignment() function which allows to
retrieve the alignment defined in the attribute and use it to use right
alignment by default but allow overriding it.

Add a test to the sample showing a non right-aligned numeric cell.

Incidentally fix a long-standing bug in wxGridCell{DateTime,Enum}Renderers
which used wxRIGHT instead of wxALIGN_RIGHT and so were not aligned properly
even by default.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@62728 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

docs/changes.txt

@@ -450,6 +450,7 @@ All (GUI):
 - Added wxEditableListBox XRC handler.
 - Added multiple selection support to wxDirCtrl (Steve Lamerton).
 - wxGrid: add possibility to prevent resizing of individual rows/columns.
+- wxGrid: allow changing the horizontal alignment of numeric cells.
 - wxHTML: add support for table borders width (Laurent Humbertclaude).
 - Added wxMouseEventsManager.
 - Building OpenGL library is now enabled by default.