refactor: rename string.require_version to string.require.

* specs/string_spec.yaml (require): A copy of the require_version
specs.
(require_version): Also check for deprecation warning on first
use.
(monkey_patch): Check that new `require` function is written into
the given namespace.
* specs/std_spec.yaml (barrel): Likewise.
(monkey_patch): Check that the deprecated `require_version` is
still written into the global namespace.
* lib/std/string.lua (require_version): Rename from this...
(require): ...to this.
(require_version): A deprecated copy of `string.require`.
* NEWS: Update.

Signed-off-by: Gary V. Vaughan <gary@gnu.org>