LineRangeSet::add_range() calls Vector::erase() in a loop over the
same vector. This could cause performance problems when there are many
selections. Fix this by only calling Vector::erase() once. I didn't
measure anything because my benchmark is dominated by another issue
(see next commit).
LineRangeSet::remove_range() also has a suspicious call to erase()
but that one is only used in test code, so it doesn't matter.
The real technical limit is with lines bigger than 2 GiB and buffers
with more than 2 Gi lines, refactor buffer loading to make it possible
to load those files.
Fix an overflow with the hash_data function at the same time
std::function is not necessary when we just want to pass a type
erased callback that does not need to own its target. FunctionRef
provides that functionality for a much lower compile time cost.
Until now, buffer had multiple recognized end coordinates, either
{ line_count, 0 } or { line_count - 1, line[line_count - 1].length }.
Now the only correct end coord is { line_count, 0 }, removing the need
for various special cases.
