TypeScript / `tsconfig.json` set `"strict": true` + refactor

[Vatroslav Vrbanic]

yeah 🤔... think about it: to do or not to do / why I haven't done in the first place? (I remember this was a decision though)

• Ok, now I remember, It was because I had to add undefined to every prop union type, it was kind of annoying in the early development phase.
• Also: Svelte development was not strict per default after Svelte 3 release, this changed recently in create-svelte.

This has to be done before next.1

[Vatroslav Vrbanic]

Current Status

svelte-check found 0 errors, 0 warnings, and 0 hints
no eslint errors / warnings

Atm still untested!

[Vatroslav Vrbanic]

Current Status

After first tests and fixes (see above) -> looking quite good! 🤞
Continuing fixing in this thread ...

[Vatroslav Vrbanic]

Current Status

svelte-check: OK ✔️ (no warnings / errors)
eslint: OK ✔️ (no warnings / errors)

So far, all "new" test-scenes are working as expected,

Next I need to adapt the rest of the old test-scenes + add some more, this will take a couple of days.
Will create new issues if I encounter some problems.