feat(create-vite): stricter TS configs in templates

[ArnaudBarre]

I started with allowImportingTsExtensions and then realised some where not enough strict and not homogenous at all.
Changes:

• Target
  • Set to ES2020 to match Vite default target, enable useDefineForClassFields because only implied if target > 2022. This avoid TS autocompleting new features that would not be widely supported like intl.formatRange or array.at. Probably we can bump some numbers for Vite 5 to include string.replaceAll and add ES2021.string to the list
  • Always include dom.iterable
• Bundler mode
  • allowImportingTsExtensions and update template accordingly
  • remove allowSyntheticDefaultImports and allowSyntheticDefaultImports: Personally I don't like using a default export when the lib doesn't explicitly set one and expecting it to work because bundler are doing crazy amount of interop.
• Linting
  • Using strict + noUnusedLocals + noUnusedParameters, I hope no debate here
  • noFallthroughCasesInSwitch is a better default because it's too easy to miss.
  • noPropertyAccessFromIndexSignature: I started using it recently and I quite like it. I'm hesitant to add it
  • noImplicitReturns: I stopped enabling this because TS correctly infer undefined on empty branches and it's annoying when having early return on callback code (like we do in Vite plugins for ex).
  • useUnknownInCatchVariables: could be added but it's really annoying to not be able to set the error type to AxiosError for ex.

Note: I did not touch the svelte config because it already extend the one from the svelte team (and I know they don't use TS the same way as I do at all)

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[bluwy]

I like the options separation 👍

[nickmccurdy]

Why were explicit extensions added? I think users generally expect bundlers to be able to resolve basic extensions. As for TS files, TS does support importing .js files by default in modules, but not .ts as they're not standard modules.

[ArnaudBarre]

The TS doesn't allow .ts was a strange move from the TS team thinking that people don't bundle code and in the meantime looking at bundling their own lib with esbuild...

This is now over with TS 5, and I really want all this resolution problems to go away so that's why I defaulted the config to use explicit extensions. This avoids a lot of syscall. Can't believe this video is 5 years old: https://www.youtube.com/watch?v=M3BM9TB-8yA