This includes the addition of the new "//go:build" comment form in addition
to the legacy "// +build" notation, as produced by gofmt to ensure
consistent behavior between Go versions. The new directives are all
equivalent to what was present before, so there's no change in behavior.

Go 1.17 continues to use the Unicode 13 tables as in Go 1.16, so this
upgrade does not require also upgrading our Unicode-related dependencies.

This upgrade includes the following breaking changes which will also
appear as breaking changes for Terraform users, but that are consistent
with the Terraform v1.0 compatibility promises.

- On MacOS, Terraform now requires macOS 10.13 High Sierra or later.

This upgrade also includes the following breaking changes which will
appear as breaking changes for Terraform users that are inconsistent with
our compatibility promises, but have justified exceptions as follows:

- cidrsubnet, cidrhost, and cidrnetmask will now reject IPv4 CIDR
  addresses whose decimal compo...