DRY attestation statement accessor methods

[bdewater]

While working on Android Key attestation format support I noticed I was writing some of these again, a quick scan of the spec showed me these all are used by at least two formats (often more) so it made sense to deduplicate these.

[grzuy]

Hi @bdewater,

Interesting.

To me it doesn't seem like "too much" repetition going on, at least as of right now.
Even some of those are not yet repeating elsewhere.

Also, not sure about making some attestation statements respond to methods that doesn't make sense to them.

In summary, I am not sure about this, at least at this moment. But I think it would be a good idea to revisit when more repetition appears definitely.

Thank you for bringing this up and opening the PR!

[grzuy]

Hi @bdewater,

I re-visited this and changed my mind.
Even added an extra commit to DRY a tiny bit more.

[grzuy]

Thanks again