[data grid] Add a recipe for correct extension of GridColumnUnsortedIcon

[michelengelen]

I think exporting it this way is not gonna work because:

1. This component GridColumnUnsortedIcon is a slot and differently exists for material and joy design systems.
2. Since this file isn't exported like export * from './GridColumnUnsortedIcon', this added export will make no difference anyways.

Possible Options:

1. We document it somehow and users keep defining on their side. (Like @michelengelen did on csb)
2. We export it from the specific design entry point, so the users will import it like
   a. import { GridColumnUnsortedIconProps } from '@mui/x-data-grid/material';
   b. import { GridColumnUnsortedIconProps } from '@mui/x-data-grid/joy';
3. Export them from the root with different names, like GridColumnUnsortedIconPropsMaterial, GridColumnUnsortedIconPropsJoy.

To me 1 and 2 feel better, 3 I would not consider since this will negate the initial idea of isolating the exports for different design systems.
For 2 though, I'm not sure if it'll be discoverable enough for the users, since it will not be obvious from what path they need to import this as we have all other exports from the root path.

Looping @cherniavskii since the problem is a bit broader, should apply to all other design system related exports. Would be nice to hear how you'd approach this. Or if you already thought around this during Joy UI support.

CC @michelengelen

Originally posted by @MBilalShafi in #11472 (comment)