Implement Analytics Engine instrumentation

[DaniFoldi]

This PR implements instrumentation for Analytics Engine datasets. Couple of questions:

• The current code records the number of indexes (which is limited to 1 by the runtime) and the first index. This index can be an arraybuffer, which isn't "portable" so right now I just call .toString. Any recommendatons for that, if nothing else we can use a TextDecoder to get some log-friendly text out of it.
• Please double-check the names of tracers, dbs, basically all string constants.

Also this PR needs some testing before I'm confident merging it.

[evanderkoogh]

I certainly wouldn't worry too much about making all the extra attributes perfect. It looks great as it is right now and if there are circumstances where we can improve some of those extra attributes, people will ask for it.

Let me know when you have had a chance to test it some more if you want. Happy to merge it as is..