refactor(lib): add types

[NiedziolkaMichal]

This PR adds strict type-checking to all files in the lib directory.

• Plugin ESLint plugin:import/typescript was added because importing types.d.ts displayed an error.
• %example-css-src% was removed from the JS editor, because none of the interactive examples uses it and it doesn't really make sense for this editor to have the ability to add CSS per example.
• Fixed some typos
• Removed {type} syntax from the docs, because it is no longer needed and in some cases stated types were incorrect.
• Changed ${page.type} to ${page} in height-builder.ts because page.type is of the type never at this point.
• Changed stats.hasWarnings() to stats.warnings in mdn-bob, because hasWarnings() didn't really provide type safety.
• Function build was changed a bit. I extracted most of the behavior to fillPageTemplate so we don't repeat outputFileSync multiple times. Cases css and js were separated because js editor doesn't support jsExampleSrc or cssExampleSrc options.
• In the getPageTmpl I have removed try/catch, so the result is never undefined. A possible error will be caught in the build function anyway.
• Function processExampleCode was split into just processJsExample and getExampleCode, because the html case was never used. The function handleDeprecatedJSExampleFormat is actually never used too, but I will remove it in a separate PR.
• Types from ./types/types.d.ts can now be used by YARI, so we can import height-data related interfaces.

[github-actions]

This pull request has merge conflicts that must be resolved before it can be merged.

[github-actions]

This pull request has merge conflicts that must be resolved before it can be merged.

[queengooborg]

There are some merge conflicts here, but once those are resolved I'd be happy to get this merged!

[caugner]

I noticed an artifact on the JavaScript demos at http://localhost:4444/pages/js/array-concat.html: 🤔

Update: Okay, I'm actually seeing this one and %example-css-src% on main and v3.4.0. 😕