Revert replacing and deprecating constants with enums

[hugovk]

Fixes #6537

Changes proposed in this pull request:

• Revert the changes in Added enums, deprecate constants #5954 (issue: Change from constants to enums #5875) as they will likely prove too disruptive for the limited benefits they bring
• While enums are good for this sort of thing, and we should use them for new code, on balance let's keep this legacy code as simple integer constants

[hugovk]

Let's close this, I somehow had glossed over that the enums were already released in 9.1.0, so this itself would be a breaking change.

Some other ideas we're considering:

• Keep the enums and deprecated ints
• Keep the enums and deprecated ints, but extend deprecation period (e.g. from v10/July 2023 to v11/Oct 2024, or even without advertising an end date)
• Provide API via both ints and enums, remove int deprecations