[styled-engine] Add back removed internal function

[mnajdova]

Fixes https://github.com/mui/material-ui/issues/44112

[mui-bot]

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[wilomgfx]

Hi, anything blocking this fix?

We just started working on the MUI 6 migration and this is blocking us from finalizing it, as the app crashes at runtime in dev.

Our workaround is:

  "pnpm": {
    "overrides": {
      "@mui/styled-engine": "npm:@mui/styled-engine-sc@6.1.7",
      "@mui/system": "6.1.7"
    }
  }