prepare release 0.42.0

[tyler-french]

This PR does not upgrade x/tools because there is a backward incompatible change that will force downstream users to upgrade.

external/io_bazel_rules_go/go/tools/builders/nogo_main.go:237:11: not enough arguments in call to pkg.facts.Encode
        have ()
        want (bool)
external/io_bazel_rules_go/go/tools/builders/nogo_main.go:399:54: not enough arguments in call to facts.NewDecoder(pkg.types).Decode
        have (func(pkg *types.Package) ([]byte, error))
        want (bool, func(pkgPath string) ([]byte, error))

We should wait to upgrade x/tools as it is pretty invasive: #3702