[input] Add missing InputBase class keys

[tianrking]

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Fixes #20706.

inputClasses already exposes the class keys inherited from InputBase at runtime, but InputClasses omitted adornedStart, adornedEnd, hiddenLabel, and readOnly. As a result, TypeScript rejected these valid keys when they were passed to the Input component's classes prop.

This change aligns the public type and generated API documentation with the existing runtime class map, and adds focused compile-time coverage for all four keys.

Tests:

• pnpm -F @mui/material typescript
• pnpm test:node Input (214 passed, 39 skipped)
• pnpm prettier
• pnpm eslint
• pnpm proptypes
• pnpm docs:api

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Deploy preview

https://deploy-preview-48940--material-ui.netlify.app/

Bundle size

Bundle	Parsed size	Gzip size
@mui/material	🔺+211B(+0.04%)	🔺+25B(+0.02%)
@mui/lab	0B(0.00%)	0B(0.00%)
@mui/private-theming	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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[ZeeshanTamboli]

I worry this would be a breaking change for developers who are using inputClasses.adornedStart etc in runtime JS and they are expecting that it is targeting .MuiInputBase-adornedStart but now with this change it will target .MuiInput-adornedStart. I agree that the types are not available on Input, but the types should match the runtime logic. But with the addition of runtime JS logic for classes, I think we are cluttering the DOM unnecessarily by having both .MuiInput-* and .MuiInputBase-* classes on the same element.

I know this is inconsistent between all three variants (filled, outlined and standard) but for the sake of not breaking anything I feel we should not do this change until the next major. However, I will keep the issue open.