Implement exemplars

[dyladan]

As far as I can tell the only thing missing for this to be done is exemplar reservoir support for views. I need to do some reading before I can pick up work on this, as I am not too familiar with it yet.

Originally posted by @pichlermarc in #2592 (comment)

Moved from views issue because it was pushed to after GA by spec

[legendecas]

FYI, there was an issue to track exemplars already #2594

[pichlermarc]

We could rename this to "Add Exemplar support to MeterProvider.addView()" to clarify.
I'm working on another issue right now which is higher priority since it this one is pushed to after GA, so this issue is still up for grabs. 🙂

[dyladan]

Duplicate of #2594