All widgets copy&pasted the same description, including an invalid reference
to "Layout", which should be "Elm_Layout".
SOME of them had been fixed over the years but this commit fixes all of them.
This significantly reduces the number of Doxygen warnings and adds meaningful
links to the docs.
I added convenience macros for check and radio, easing discoverability
in C.
This will avoid C# issues such as:
lib/elementary/elm_pan.eo.cs(14,23): warning CS0108: `elm.Pan.CHANGED'
hides inherited member `efl.Gfx.CHANGED'. Use the new keyword if hiding
was intended
lib/efl/interfaces/efl_gfx.eo.cs(24,23): (Location of the symbol related
to previous warning)
Since nstate is not a legacy widget, I can safely change the event name
and the test case.