Fix mysqli_fetch_* stubs

[kamil-tekiela]

I have just noticed during testing that I have specified the wrong type in the previous PR. While correcting it, I also decided to provide more specific types. I am not sure if the types for mysqli_fetch_array() works this way, but I hope it does.

[orklah]

Can you use the occasion to fix the indentation in mysqli stub? :)

[kamil-tekiela]

I fixed the indentation and I have also decided to properly specify the type. The type is taken from fetch_column() - false. In the case of MYSQLI_NUM it will be a list. In the case of fetch_all() it is always a list of one of the three options.

I have also noticed I forgot to fix fetch_fields()

[weirdan]

Thanks!