Aml: Add fold/level_fold/find_map iterators and lookup handle->name

[rw-vanc]

I only really needed reverse name lookup, but I implemented some iterators along the way. fold and find_map iterate over all values. find_map does a sort of short circuit to reduce the number of visits, but does not necessarily stop on the first correct result. level_fold is similar to traverse but returns a value.

[martin-hughes]

I think this PR has got a bit stale for merging - e.g. it still references AmlHandle which isn't in the latest versions. There doesn't seem to have been much demand, so I'll close this, but with a few comments:

• Thank you for this PR (and others!) @rw-vanc
• Since the various function names largely match those within Iterator, my feeling is it'd be better to provide an implementation of Iterator. I'm not sure how that would work with the separation between levels and children, quite happy to bikeshed if you or anyone wants to take it further!
• If not implementing Iterator, then the only non-public access any of the code needs to Namespace is to root in level_fold. I think it could take a non-mut reference throughout, but I'm less familiar with older versions of the crate
  • alternatively add a get_root() method and make these plain (rather than member) functions (but perhaps that's the old fashioned C++ bod in me talking)