Use ESM build of vite

[pddg]

npm test shows following warning message.

The CJS build of Vite's Node API is deprecated. See https://vitejs.dev/guide/troubleshooting.html#vite-cjs-node-api-deprecated for more details.

It seems that package.json in root does not have "type": "module" and vite.config.ts is used. I did following:

• Add type: module to package.json in root
• Rename all vite.config.ts to vite.config.mts
• Rename all vite.config.ts in some files to vite.config.mts
• Complete extension of relatively imported files in vite.config.mts
  • Maybe, this is not required.
  • Discussed here: https://github.com/siefkenj/unified-latex/pull/90#discussion_r1510140395
• Update some actions used in CI
  • Some actions are using Node v16

[siefkenj]

Thanks for this! I think the cleaner solution is to add type: "module" to the root package.json. Could you modify this PR to do that instead?

[pddg]

Sure. Unnecessary commits were removed and force pushed.

[pddg]

Edited comments for clarity of changes.

[siefkenj]

Thanks for the fix!