diff: highlight word-level changes in git diffs

[yuja]

default style:

with bg color:

Checklist

If applicable:

• [x] I have updated CHANGELOG.md
• [x] I have updated the documentation (README.md, docs/, demos/)
• [ ] I have updated the config schema (cli/src/config-schema.json)
• [ ] I have added tests to cover my changes

[joyously]

I can't see the underscores with the underlines. How is that second image using bg color? I see only black bg.

[martinvonz]

I can't see the underscores with the underlines.

I agree they're not easy to see. Try zooming in a bit.

How is that second image using bg color? I see only black bg.

Only modified parts, such as the added use line, use background color.