Made column and row spans members so they don't interfere with app-defined properties.
Added identifier to wxRichTextObject so objects can be addressed by name.
Generalised wxRICHTEXT_CHANGE_OBJECT command so it can now apply to a paragraph as well as an object within a paragraph.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@75124 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775