x/tools/gopls: modernize should simplify func calls which always return nil errors now

[mvdan]

For example, as of Go 1.24, https://pkg.go.dev/crypto/rand#Read always returns a nil error on all platforms, so any callers like

_, err := rand.Read(b[:])
if err != nil {
        return nil, err
}

can be modernized and simplified to just

rand.Read(b[:])

I'm sure there are other instances where standard library APIs can never fail. Another one that comes to mind is the various io.Reader and io.Writer methods on bytes.Buffer, or some of the methods on strings.Builder.

[prattmic]

How does the tool decide which functions can never return an error? Hardcoded list? Special comment? Hyrum’s law assumption that anything that doesn’t return an error today can never add one?