cty's new "refinements" concept allows us to reduce the range of unknown
values from our functions. This initial changeset focuses only on
declaring which functions are guaranteed to return a non-null result,
which is a helpful baseline refinement because it allows "== null" and
"!= null" tests to produce known results even when the given value is
otherwise unknown.
This commit also includes some updates to test results that are now
refined based on cty's own built-in refinement behaviors, just as a
result of us having updated cty in the previous commit.
* Updating the license from MPL to Business Source License
Going forward, this project will be licensed under the Business Source License v1.1. Please see our blog post for more details at https://hashi.co/bsl-blog, FAQ at https://hashi.co/license-faq, and details of the license at www.hashicorp.com/bsl.
* Update copyright file headers to BUSL-1.1
---------
Co-authored-by: hashicorp-copywrite[bot] <110428419+hashicorp-copywrite[bot]@users.noreply.github.com>
