Fixes#1433 although in a slightly different way than requested:
We ensure that scrolloff *displayed* lines are visible below the
cursor, not scrolloff *buffer* lines.
Instead of highlighting full lines and then trim them to make them
fit in the window, highlight only the visible portion, and rely on
the compute_display_setup system introduced for wrapping to setup
our buffer range correctly
update-option will make the range-descs and line-descs option up to
date with the latest buffer modfications, changing the ranges/lines
to where they moved according the modifications since the timestamp
on the option.
Generalize this option type, which is a timestamped list of
<line number>|<arbitrary string>. That way this type is not strongly
coupled with the flag-lines highlighter, and can be reused for other
use cases.
range-faces are now used to replace-range highlighters, where the string
part is not interpretted as a face but as a display line, so the name was
not relevant anymore.
replace-ranges is takes a range-faces option, but treats the face
string as a display line to be parsed, and replaces the range display
with this display line.
Highlighters now run in 3 phases:
Wrap, Move, and Colorize. That way we guarantee the wrap
highlighter runs first, then eventual line numbers/flags,
and finally the colorizers.
We also run a `compute_display_setup` method thats responsible
for computing the lines that will be displayed, eventually
scrolling the view to ensure the cursor is visible.
That means we wont have a very nice interaction between show_whitespaces
and column highlighters, but thats the simplest fix for now, if we want
a better behaviour we need to introduce a way to know that a replaced
range is splittable (meaning it means to have the same amount of columns
as the range it replaces)
Fixes#1275
We were still adding one more char to the line number width in case
it would contain a minus sign. The minus signs are not used anymore
in relative line numbering so we dont need to keep that addtional
char which is always a blank.
