[code-infra] Move `@mui/internal-test-utils` to code infra repo

[Janpot]

• [ ] I have followed (at least) the PR section of the contributing guide.

[mui-bot]

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https://deploy-preview-47422--material-ui.netlify.app/

Bundle size report

Bundle	Parsed size	Gzip size
@mui/material	0B(0.00%)	0B(0.00%)
@mui/lab	0B(0.00%)	0B(0.00%)
@mui/system	0B(0.00%)	0B(0.00%)
@mui/utils	0B(0.00%)	0B(0.00%)

Details of bundle changes

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