Various cleanup, fixes and XML docs comments

[stevejgordon]

This is a varied bunch of cleanup initially started when replacing XML todos with meaningful documentation.

We've removed the concept of setting ActivitySource and Meter names on our options. This is now confusing, and it's better to prefer the Otel native way to manage that. This also means a few other overloads that worked with params string[] can now be removed.

Now that we accept a log file directory env var and when present, enable the file logger, some of the redundant code could be removed. We no longer need a default directory and only log if this is explicitly set.

Removes a few unused types.

Log messages were updated to reflect new type names. Some were removed and event IDs were also deduped.

Some classes that I don't expect us or consumers to extend are sealed.

[Mpdreamz]

LGTM!