proposal: x/crypto/cryptobyte: add ReadUint32LengthPrefixed

[AGWA]

Proposal Details

cryptobyte.String has ReadUintNLengthPrefixed for N 8, 16, and 24, but not 32, despite Builder having AddUint32LengthPrefixed.

ReadUint32LengthPrefixed would be useful for parsing SSH protocol messages, which use uint32-prefixed strings.

I propose adding:

func (s *String) ReadUint32LengthPrefixed(out *String) bool

cc @rolandshoemaker @FiloSottile

[FiloSottile]

Sounds good to me.

[AlexanderYastrebov]

I implemented it two years ago https://go-review.googlesource.com/c/crypto/+/360095 but it was never reviewed.
Somehow original issue link #49227 is not working atm.