Reduce bundled size of diff package

[fisker]

Description

standalone.js

520 -rw-r--r-- 1 fisker None 529175 Jan 27 10:45 main.js
500 -rw-r--r-- 1 fisker None 509950 Jan 27 10:46 working.js

~ 20k

bin-prettier.js

440 -rwxr-xr-x 1 fisker None 449592 Jan 27 11:11 after.js
476 -rwxr-xr-x 1 fisker None 486907 Jan 27 11:09 before.js

~ 36k

Checklist

• I’ve added tests to confirm my change works.
• (If changing the API or CLI) I’ve documented the changes I’ve made (in the docs/ directory).
• (If the change is user-facing) I’ve added my changes to changelog_unreleased/*/XXXX.md file following changelog_unreleased/TEMPLATE.md.
• I’ve read the contributing guidelines.

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