Split dialect

[Erikvv]

sqlgen: split dialect file

Organize runtime dialect functions into one source file per dialect for better navigability. In preparation to add another function.

Change is on top of https://review.dev.storj.io/c/storj/dbx/+/9312, only review the last commit of this branch.

I'm no longer working for Storj but I'm trying to see if I can wrap up the change which was close to being finished.

[egonelbre]

@Erikvv btw. with regards to the implementation, was there a reason you weren't sharing the postgres rebind implementation and instead copying the implementation?

e.g. the implementations could be:

type pgxcockroach struct{}

func (p pgxcockroach) Rebind(sql string) string {
    return postgres{}.Rebind(sql)
}

[Erikvv]

@Erikvv btw. with regards to the implementation, was there a reason you weren't sharing the postgres rebind implementation and instead copying the implementation?

I've only moved the code, not de-duplicated. Sounds like a good improvement.