🐛 Position more pairs of lines "opposite" each other in side-by-side view

[dandavison]

I'm thinking that we should make more effort to position certain pairs of lines at the same level, where that makes sense -- the first hunk here would be an example. Would you agree @th1000s?

In terms of the current implementation, IIRC the issue is that a and b are not recognized as "homologs" because they are not deemed similar, according to a distance metric which is basically edit distance divided by length of longer string.