[code-infra] Use @mui/docs where possible

[LukasTy]

Related to mui/material-ui#42833.

Would allow dropping last re-exports of MarkdownElement, Link and HighlightedCode.

Also, ditch @mui/docs aliasing from monorepo as there is already a dependency with that name (related to mui/mui-x#13713).
We agreed to keep the alias to avoid potential problems with out-of-sync @mui/docs and @mui/monorepo.

[LukasTy]

import { SectionTitle } from '@mui/docs/SectionTitle'; probably worked only because of the present alias.
Bumped the dependency version where this component is exported.

[Janpot]

The alias for @mui/docs was intential as there is still a high coupling between docs code and @mui/docs. Unless this unblocks a specific problem I would be inclined to keep it until all imports from @mui/monorepo/docs/... are removed from Toolpad/X docs

[Janpot]

Thank you 🙏