Provide a method for determining center locations of children on a block

[drewj-tp]

I know this isn't part of your design, but maybe this method could take an optional flag parameter that defaults to Flags.CLAD. That way, if in the future someone wants to use some other flag to identify what they want to define as a "pin".

This request is scope creep, but it seems like a one-line change and a single unit test to make this more extensible in ways that you have convinced me are important.

Thoughts?

Originally posted by @john-science in #1943 (comment)

[john-science]

This was originally a comment on Block.getPinLocations(), to just add a input flag to make this method more flexible.