Deprecate lowercase enums in BaseEnum

What does this MR do?

Deprecates the lowercase versions of enums. Issues raised before in #31585

Works towards #258544, which aims to deprecate the existing lowercase enums.

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Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• Separation of EE specific content

Availability and Testing

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• Tested in all supported browsers
• Informed Infrastructure department of a default or new setting change, if applicable per definition of done

Security

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