Deprecate utilities in favor of ign-utils

[chapulina]

The ign-utils package has been created to hold general purpose utilities that have minimal dependencies and are useful for multiple libraries. We've already moved the SuppressWarning functionality there.

I think we should also move the ExtraTestMacros and to ign-utils and deprecate the utilities component of this package. I can see an argument for keeping that here close to other test configurations though. My main concern is that this repository is not well suited to hold C++ code. We have created a new namespace, utilities, which doesn't match the rest of this library. We aren't generating test coverage for it, etc. I think it's a cleaner separation of concerns if we leave C++ code out of ign-cmake.

Desired behavior

On ign-cmake3, using ignition::utilities generates deprecation warnings. On ign-cmake4, the component is removed.

I suggest this with the full understanding that ign-cmake4 may only be released in 2078 🙃

My short-term suggestion is to migrate these utilities to ign-utils and stop using the ones from ign-cmake, even though they're not officially deprecated on ign-cmake2.

Alternatives considered

We could just keep ExtraTestMacros here... That would certainly involve less effort. My main concern is that we forget the separation of concerns and start adding more header-only functionality here, when it should go to ign-utils.

Implementation suggestion

1. Add ExtraTestMacros to ign-utils
2. Migrate all uses of utilities to use ign-utils
3. Remove all dependencies on the utilities component from Fortress
4. Initiate the tick-tock of utilities suggested above.

Additional context

See #18 for why the utilities were added in the first place.

[mjcarroll]

This copies ExtraTestMacros into ign-utils: gazebosim/gz-utils#37

[chapulina]

Fully deprecated as of #233