Final is more granular, it consists of FinalFg (f), FinalBg (g)
and FinalAttr (a) which control if a face's fg, bg, or attributes
fully overwrite the previous face (instead of merging) and if
following faces apply on top of this face or not.
Fixes#2388 if the Whitespace face has the FinalFg flag.
When on an end of line, certain behaviours can be surprising, for
example delete will join the following line (which makes sense, and
is consistent, but hard to predict if we do not know the cursor is
on and end of line).
As Kakoune is moving more and more towards treating end of lines
as any other character, making it clear when the cursor lies on
them seems like a good way to reduce surprise.
