gh-150045: Add frozendict support to the compiler and AST constants

[lgeiger]

This adapts the compiler to treat frozendict as a valid constant similar to frozenset:

• 37d8189 adds frozendict to ast constants
• b027839 adds support for deduplication via _PyCode_ConstantKey
• 992b4b6 adds recursive constant merging which make
• aeed04a fixes the freethreading case

Let me know if you'd like me to split this up into separate PRs, this has become a much larger than I had originally intended.

• Issue: Add support for frozendict as AST Constant #150045

[picnixz]

The consensus on the issue is not reached and there is still opposition, hence marking as pending.

[github-actions]

This PR is stale because it has been open for 90 days with no activity.