[utils] Allow nested imports in @mui/utils to speed up build

[flaviendelangle]

Part of #35840

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

See mui/mui-x#9172 for context
I also took the opportunity to migrate some files to TS

One step toward #35840

[mui-bot]

Netlify deploy preview

https://deploy-preview-37586--material-ui.netlify.app/

Bundle size report

No bundle size changes

Generated by 🚫 dangerJS against a78c098

[michaldudak]

LGTM

[NMinhNguyen]

@flaviendelangle previously, a lot of the exports had the unstable_ prefix but with the way the files/folders are after this PR it’s possible to import @mui/utils/useEventCallback without the unstable_ prefix - is that a concern?

[flaviendelangle]

Do you have an import from the same endpoint that has changed?
Or is it just on the new endpoints (@mui/utils/useEventCallback for example) that you don't have the unstable_ prefix?
If so, maybe @michaldudak can give his point of view 👍

[michaldudak]

IMO we should discourage developers from importing from @mui/utils directly and treat this as an internal package. Individual functions that could be made public should be reexported from other packages.

[NMinhNguyen]

Or is it just on the new endpoints (@mui/utils/useEventCallback for example) that you don't have the unstable_ prefix?

This :) what I mean is that in index.js there is aliasing happening that re-exports some of the utils with that prefix, but the nested imports don’t follow that convention currently.