Documenting primtypes, round 1: ByteArray# and Array#

[Hécate]

Hi everyone,

With the sunny days back in this hemisphere, so do the documentation MRs.

I have two primtypes for which I'd like some help / review / interesting 
information:

* ByteArray#: This is mostly done, you can observe the current rendered 
draft documentation here: 
https://gitlab.haskell.org/ghc/ghc/-/merge_requests/8067#note_425560
    Please note that the free-floating "Byte Arrays" section of 
documentation cannot be exported or re-exported by GHC.Exts, so we're 
pretty much left with what's in the types' documentation;

* Array#:  The ticket is here: 
https://gitlab.haskell.org/ghc/ghc/-/issues/21462
    State of things: In terms of documentation, we have no 
documentation. Some stuff can be inferred from the SmallArray# haddocks 
but I doubt that every property / interesting usage / pitfall can be 
reasonable derived from putting ¬ at the beginning of the SmallArray# 
documentation.


Now, on an unrelated note, I'm also wondering about the fate of 
GHC.Pack, for a number of reasons. You will find the ticket here: 
https://gitlab.haskell.org/ghc/ghc/-/issues/21461.


My thanks to everyone who's helped me so far, with a special mention to 
bodigrim and koz ross.

Cheers

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