[code-infra] Convert @mui/utils to typescript

[Janpot]

Trying to get a feel on how we can leverage Claude code to help us finish the typescript migration

Prompt (inside packages/mui-utils):

This folder contains a package that is in transition from js to ts. Some of the files are written in plain js and have an accompanying .d.ts file. it is your task to finish the conversion. concretely, in ./src, you must rename the .js files to .ts(x) (use git mv), then look at the content of the relevant .d.ts file and integrate its types into the freshly created ts file. It's important that functionally everything stays the same, meaning after type erasure, the ts file needs to be exactly the same as the original js file. and the exported types must be equal to the original .d.ts files. you can fix type issues local to each file (pnpm typescript runs a type checker). you don't need to keep the .d.ts files

Next time, need to make it clearer that it's not supposed to functionally change the code. It's only allowed to operate at the type level. Also need to explain that some js files contain jsx, so these need to get a tsx extension. It did get somewhat trigger happy altering code, so had to carefully review and make a lot of tweaks.

[mui-bot]

Netlify deploy preview

https://deploy-preview-45671--material-ui.netlify.app/

Bundle size report

Details of bundle changes (Toolpad)
Details of bundle changes

Generated by 🚫 dangerJS against 5fcc5d4