[docs] Add hexToRgb rename to v3 to v4 changelog

[zettca]

Closes #18995

• I have followed (at least) the PR section of the contributing guide.

[mui-pr-bot]

No bundle size changes comparing 2a60cfc...e7bfb49

Generated by 🚫 dangerJS against e7bfb49

[oliviertassinari]

@zettca It's a great first pull request on Material-UI 👌🏻. Thank you for working on it!

[mbrookes]

This change implicitly suggest that the colorManipulator functions are public, when they aren't supposed to be. See: #13039.

[oliviertassinari]

At this point, I think that they are public, we import them from the demos:
https://github.com/mui-org/material-ui/blob/d9ced3a2102c9e7441b15bb76d5d9bdbaf9391de/docs/src/pages/components/progress/CustomizedProgressBars.tsx#L2

A developer can do:

import { hexToRgb } from '@material-ui/core';

---

Side note. When is a module considered public? I think that when it's exported from the barrel index, which is the case.

[mbrookes]

Okay. It's a shame the fade name change wasn't applied first in that case. One for v5?

[oliviertassinari]

I don't see what you are referring to. But no objection to consider changes for v5.

[mbrookes]

As per the issue linked from the comment you replied to earlier today: #13039 (comment)

[oliviertassinari]

thanks, sounds great