Various places in Kakoune code used to modify selections so that
cursors would not lie on an end of line. Remove those to increase
Kakoune's consistency and simplicity.
Now that end of lines are highlighted separately, they should not
be handled specially in most commands.
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.
That means we can now have highlighters active at global, buffer, and
window scope. The add-highlighter and remove-highlighter syntax changed
to take the parent path (scope/group/...) as a mandatory argument,
superseeding the previous -group switch.
