ENH: move the recursive collect_asset_docs up to Device

[tacaswell]

While talking to @jklynch about how asset document collection works I noted that the recursive fallback was implemented in the AreaDetector related classes. As part of a push to refactor and (hopefully) simplify how we manage external resources it would be good to pull the recursive discovery and accumulation up to the Device level.

[ZLLentz]

This looks very sensible :+1:

Functionally, there's a small change here of only checking kind='normal'- could that be related to some of the area detector test failures?

[ZLLentz]

This looks very sensible :+1:

Functionally, there's a small change here of only checking kind='normal'- could that be related to some of the area detector test failures?

[tacaswell]

rebased and tweaked the test a bit.

It makes sense that collect asset docs and read should hit the same children.

[tacaswell]

Yup, this is super broken and I have no idea why :(

I assume multiple inheritance is involved....