[core] Fix @mui/material package building

[timbset]

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

Hi there.

I found out that material package built folder structure has changed unexpectedly since 5.10.3. I have researched and found that there were no reasons for that kind of change and the problem is in adding a new file to the package root in this PR: #32735 that affects this part of the building script. While learning changes I did not found any reason why this should stay as it is, I event did not find any usage of this file. So my idea is to remove files from the root by putting it into a folder, so the building algorithm is going to perform as it was before 5.10.3.

Why is the folder structure important to me? Well, I try to use best practices of using material-ui and one of them is to import specific component by a specific path instead of importing the whole package. Unfortunately, this approach does not work with ESM that is necessary for me. That's why I've reported the issue. Until it is fixed, I have to resolve all imports to a specific files in the package. I know that you do not promise that internal files are not going to be changed, but I also hope that all your changes are reasonable. The current one is not.

By the way, I don't pretend to be right about fixing the issue this way. So my main goal is to rollback a building algorithm.

[mui-bot]

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📖	Netlify deploy preview: https://deploy-preview-35324--material-ui.netlify.app/

@material-ui/core: parsed: -16.44% 😍, gzip: -10.10% 😍
@mui/material-next: parsed: -6.48% 😍, gzip: -4.44% 😍

Details of bundle changes

Generated by 🚫 dangerJS against c9c6872

[mnajdova]

Thanks for the detailed description on the PR. The goal of #32735 was to provide augmentation for simplifying some types to allow better TypeScript checks. The reason why it was added as a root was so that the import for the file would be consistent with other imports. Now the import needs to look like:

import "@mui/material/types/OverridableComponentAugmentation";

but honestly I am ok with it. We probably want to leave a comment in #19113 with the change once this gets merged.