standardize naming of 'no-op' aggregators

[clintropolis]

Resolves #6934 by prefixing all 'no-op' aggregators with Noop to follow convention of built-in NoopAggregator and NoopBufferAggregator

[clintropolis]

Since I'm renaming a few files in the area already, any upvotes for renaming some of the other datasketches extension post-aggregator types to make navigating to the right file easier? I would like to switch around what is currently the middle of the compound name to the front, like ArrayOfDoublesSketchToNumEntriesPostAggregator -> NumEntriesArrayOfDoublesSketchPostAggregator

(Open to other ideas too)

[jihoonson]

Should EmptySequence and EmptyIterator also be renamed?

Since I'm renaming a few files in the area already, any upvotes for renaming some of the other datasketches extension post-aggregator types to make navigating to the right file easier?

I think it depends on how many classes you are thinking to rename. I'm fine by doing it in this PR if it's small enough.

[clintropolis]

Should EmptySequence and EmptyIterator also be renamed?

I don't think so, since maybe 'empty' more correctly describes those cases.

I think it depends on how many classes you are thinking to rename. I'm fine by doing it in this PR if it's small enough.

I think that would be more appropriate to do in a different PR if at all.

Thanks for review!

[jihoonson]

Thanks. LGTM!