add Dragonfly to ProductVariant (#3199)

* add Dragonfly

* add Memurai and Redict to ProductVariant

* add KeyDB without Version

* Track the new ProductVariant members as unshipped, and simplify KeyDB detection

New enum members belong in PublicAPI.Unshipped.txt, not directly in
Shipped.txt (which should only reflect what's actually released).
Also collapse the KeyDB executable check into a switch pattern guard.

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Co-authored-by: Marc Gravell <marc.gravell@gmail.com>