PEP 814 -- Add frozendict built-in type

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Please consider PEP 814 -- Add frozendict built-in type https://peps.python.org/pep-0814/

• [x] The PEP has been discussed in threads listed in its Post-History header
• [x] The PEP was announced on Discuss (link in Post-History)
• [x] The PEP includes all relevant Suggested Sections
• [x] The PEP includes endorsements from the projects/groups/people it helps
• [x] The PEP has a CODEOWNERS entry

SIG-specific:

• [ ] Typing PEPs: link to the Typing Council's recommendation for the PEP:
• [ ] Packaging PEPs: don't file the issue here, ask the delegate (Paul Moore) on Packaging Discourse