Consider adding static IteratorEnvironment.builder method

[dlmarion]

Consider adding IteratorEnvironment.builder() method that returns a ClientIteratorEnvironment.Builder object. At this point, we might want to rename ClientIteratorEnvironment to DefaultIteratorEnvironment, just be aware that there was a class with this name already and it was removed.

[dlmarion]

While working on #5587 I created SystemIteratorEnvironmentImpl because the server side iterator environment has some behavior differences vs the client side iterator environment. Creating one, default, iterator environment for use in the client and server code might not be feasible.

[dlmarion]

Closing as I don't think it will be possible to create a single static method that returns a Builder.