Remove ObjectCreator from main cdda solution

[akrieger]

Summary

None

Purpose of change

@ZhilkinSerg made a comment in #60385 which made me go back and verify some assumptions I'd made when adding ccache support. I thought the only way to get rid of the separate ObjectCreator build would be to add it to the main cdda solution because Visual Studio wouldn't reuse artifacts between solutions, even for the same project. MSBuild, however, is not Visual Studio and will happily do so, as I found out earlier when playing with some changes. Removing ObjectCreator from the main solution helps in the general case because it reduces the disk space usage and overhead of the easy 'build solution' button and other ways one can accidentally trigger building ObjectCreator from VS.

Describe the solution

Remove ObjectCreator from the main cdda solution. In the msvc-full-features workflow, call msbuild twice to build first cdda & tests, and secondly ObjectCreator itself from its own solution. This works A-OK.

Describe alternatives you've considered

Testing

https://github.com/akrieger/Cataclysm-DDA/actions/runs/3124402835/jobs/5067727146 passed and did the sensible thing when pushed to my repo.

Additional context