feat: add rule for deprecated rand.Seed in Go 1.20

[dnwe]

Ref: https://pkg.go.dev/math/rand#Seed

[dnwe]

Although now I think about this, that autofix doesn't really make sense because rand.Seed is explicitly initialising the global generator (with the assumption being that the global generator is used somewhere else in the program) whereas the replacement rand.New(rand.NewSource(...)) relies upon you using the returned Rand from that call

[dgryski]

You don't to have a "suggested" fix. You can just leave it as a warning, or maybe reference courses of action in the message.

[dnwe]

@dgryski yep — although I think staticcheck will already report warnings for any use of funcs marked // Deprecated: so the benefit here was mostly being able to autofix things.

I wonder if we can do anything better with a pair of rules here as I'm assuming there were two historical uses of rand.Seed:

1. people were calling rand.Seed with a timestamp or something "random" to result a non-deterministic sequence of pseudo-randomness from the generator — those calls can now be removed from the source in Go 1.20 and newer as it is already seeded randomly at startup and we could do that removal with an autofix
2. people were calling rand.Seed with a constant number to explicitly cause deterministic sequence of randomness, they can given a warning with rand.New(rand.NewSource(...)) pointed to as the solution

I'm not sure how easily we could detect case 1 though