feat: update to kit@next.100, convert to esm

[jthegedus]

Summary

SvelteKit has changed a lot in the last ~40 versions of the Beta, this PR brings this Adapter compatibility up to version @svelte/kit@1.0.0-next.100

Fixes #37, fixes #38

Full list of changes:

• document bug caused by If files.assets === 'public', Vite copies the directory's contents sveltejs/kit#587
• use esbuild in place of files/index.cjs and utils.copy_server_files as the Vercel/Netlify etc adapters do since Adapter bundle sveltejs/kit#1091
  • this should solve an error where the produced app.mjs imports @sveltejs/kit but it is not included in the Cloud Functions package.json fixing Container crashes on cloud run #38
• support fetch with import '@sveltejs/kit/install-fetch fixing Svelte Fetch is not included on the Firebase build #37
• DRY the handler rename and copyFileSync code in each of the Function and Run adapt funcs
• use utils.rimraf to clear the output dirs before writing (removes files that would not be overridden)
• update handler.js to use SvelteKit Http utils instead of the deprecated app-utils package
• add TS type declarations for this adapter
• update adapter dev env to use Node.js 16 and pnpm v6
• list adapter version and kit version compatibility table

[github-actions]

🎉 This PR is included in version 0.6.0 🎉

The release is available on:

• npm package (@latest dist-tag)
• GitHub release

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