Add flags to show/export defineable values and warn if a -define is unused in the project

[laytan]

[DragosPopse]

-show-defines and -export-defines?:)

[laytan]

To me, a define is something that is defined, and a defineable something you can define. I do agree it is not a very ergonomic name though.

[laytan]

I've rebased and improved the PR. Now it also collects doc comments tied to the declaration if available, this also needed a change to the way it is shown because those can be multiline.

Here is what it looks like now when I added -show-defineables to a odin test invocation:

I am open to ideas to improve that.

And maybe the name should be -show-defineable instead of with the s added, or an entirely different name?

[Feoramund]

And maybe the name should be -show-defineable instead of with the s added, or an entirely different name?

-show-config?

I only just now became aware of this PR, otherwise I would've chimed in earlier. This is a nice feature though.