Change Result#each to return an Enumerator when called without a block.

As with #10992, this lets us call #with_index, etc on the results.
When .find_each is called without a block, return an Enumerator.

This lets us do things like call: .find_each.with_index
Merge pull request #10993 from Empact/result-each-enumerator

Change Result#each to return an Enumerator when called without a block.
Merge pull request #10992 from Empact/find-each-enumerator

When .find_each is called without a block, return an Enumerator.