Support span/resource/metric types

[thisthat]

This PR makes the following contributions:

• Add more tests
• Verifies that attributes used in AnyOf constraints are correctly defined
• Add initial support to differentiate YAML semantic convention between span, metric, and resource

@justinfoote please, have a look :)

[Oberon00]

Ideally, we should minimize the unit test files. Right now they contain quite a lot superfluous code.

I think you should add the tests in a separate PR beforehand, so we can also see what changes in expectations, etc. with the functional changes in the follow-up PR.

[justinfoote]

:awesome: There's a lot here. I'll pull this down and review it soon!

[Oberon00]

Approving this because we used this internally at Dynatrace for some time with success.

[justinfoote]

I started a full PR review, but there's a lot here, and I don't think I've fully processed what all of the tests are doing.
In addition, the style of testing is considerably different between my earlier PR (which used pytest) and this one (which uses unittest). The result is that this repo is kind of a mess, but maybe that's OK for a build-tools project.

I'd love to see us come back and refactor and clean this up in the future.
And we'll need a followup PR to support metrics.

But given those caveats, I approve.

[thisthat]

@justinfoote I know about the different testing styles. We wrote these tests while developing the tool and, honestly, changing them was too much of an effort for this project 😅

[Oberon00]

The result is that this repo is kind of a mess, but maybe that's OK for a build-tools project.

I think it's not really OK but we can IMHO live with it, as it's still better than fewer tests.

[arminru]

That's a good idea! Otherwise we'd end up with a broken spec build since the version is not pinned and we don't define types there yet.