Merge #10925

10925: minor: Simplify `.vscodeignore` r=lnicola a=lnicola

The quadruple negation we used to have here was quite confusing:

```gitignore
**
!out
out/**
!out/src
```

Let's ignore everything and cherry-pick what we want to include.

~~And also include the extension sourcemap, just in case someone wants to debug the extension.~~

Co-authored-by: Laurențiu Nicola <lnicola@dend.ro>