Add info about cause explicitly always being undefined

[KATT]

Summary

Adds info that cause is always undefined.

Motivation

• I was confused, I guess I missed that [string]: any and interpreted this as .cause being supposed to be set.
  • 
  • [Discussion] Intentional to mask error.cause? #123
• Never serialize .cause Errors, rely on message + stack summary instead #110

Further comments

I am not sure if I agree with the decision to hide it, the original issue (#94), seemed to want explicit handling of .cause and not to hide it. It caught me by surprise.

[voxpelli]

I am not sure if I agree with the decision to hide it

It aims for readable output rather than verbose completeness

[mcollina]

I think types are likely better be lenient instead.

[mcollina]

I don't understand this change.

[voxpelli]

@mcollina Without this change accessing .cause will match [key: string]: any; whereas its actually not any, it's known to be never / undefined

[mcollina]

@voxpelli do you agree with this change?

[voxpelli]

I generally agree with it, yeah, I do would prefer the cause?: never instead though

[mcollina]

@KATT could you make it to be cause?: never?

[KATT]

Apologies about the delay - GitHub notifications are 💀 , I've updated it now