[docs-infra] Allow {{"component": “}} to import from same markdown folder

[oliviertassinari]

Summary

Having to the component source outside of the markdown folder like in https://github.com/mui/material-ui/blob/master/docs/data/material/all-components/all-components.md is not great. You want to be able to delete a page of the docs and all its related content all at once (closer folders).

Examples

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Motivation

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Search keywords: -

[flaviendelangle]

Follow up on #34243

[oliviertassinari]

To provide more details on the problem, the goal is to have the .js file and the markdown in the same folder but:

1. The use of {{"demo": resets the theme to use the default of Material UI, which isn't the theme of the docs. So ❌
2. The use of bg:"inline" doesn't include a padding on mobile, this needs to be added back ⚠️
3. The use of {{"component": doesn't allow to import the components from the same folder as ``{{"demo":` would So ❌

We could solve this in different ways:

• a. support import path from a higher level, by fixing 3
• b. have a demo flag to keep the default theme and another one for the layout. But I get the feeling that it's what {{"component": vs. {{"demo": is all about. So option a. might make the most sense.