Export core identifiers

[wilwade]

Problem

sdk.core.identifiers were not exported, but they should be for people to use them

Solution

Added it to the exports

Double Checks:

• [x] Did you update the changelog?
• [x] Any new modules need to be exported?
• [x] Are new methods in the right module?
• [x] Are new methods/modules in core or not (i.e. porcelain or plumbing)?
• [x] Do you have good documentation on exported methods?