Filter-out context-only hunks in our range-diff

[Urgau]

This PR filter-out context-only hunks in our range-diff.

We currently only hide-by-default file changes that only have context-only changes, but as described in #2394, a range-diff might have plenty of hunks that only have context changes (ie not a diff line, +/-).

Currently (with context-only changes)	Currently	This PR

Implementation wise, I had to copy and lighting edit the UnifiedDiff implementation from imara-diff in order to be able to filter-out some hunks.

I sadly had to remove the checkbox (not sure it was very useful to begin with) as knowing with lines to show/hide is highly non-trivial for context line as they can be part of the same context for multiple hunks at the same time (each hunk has +- 3 context line).

I also took the opportunity to switch to gix-imara-diff since the original crate has had unreleased fixes for several months.

Testing link: http://localhost:8000/gh-range-diff/rust-lang/miri/98cb1d3d48fa7c8e97994050bfd69e8f3da2a1a7..3f8007e19b8cac3d08fb07579bde3217c58807e4/e0b3afbdd5362aa348abc6661ed6417d1a21f58c..d811aaf958594156e2ce38365b835c361aa88de9

Fixes #2394
cc @RalfJung

[Kobzol]

Can't say I could examine the hunk algorithm in detail at the moment, but the output looks reasonable, and the filtering of non-interesting hunks seems valid.

View changes since this review

[Urgau]

Can't say I could examine the hunk algorithm in detail at the moment

I wouldn't expect you to do it, I didn't examine it in detail my-self.

The only different between our version and the one in the crate is that we give &[Hunk] instead of &Diff, so we can filter-out some hunks, the rest is strictly the same.