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

[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.