log/slog: built-in handler constructors take options as a second arg

log/slog: built-in handler constructors take options as a second arg

There is now one constructor function for each built-in handler, with
signature

    NewXXXHandler(io.Writer, *HandlerOptions) *XXXHandler

Fixes #59339.

Change-Id: Ia02183c5ce0dc15c64e33ad05fd69bca09df2d2d
Reviewed-on: https://go-review.googlesource.com/c/go/+/486415
Reviewed-by: Alan Donovan <adonovan@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Run-TryBot: Jonathan Amsterdam <jba@google.com>