The same as D14610 but for native. Verifies prekey signatures and regenerates prekeys when it's invalid.

Depends on D14620, D14610

Triggered PrekeysHandler on native; used Xcode debugger and additional logging to confirm:

• For valid prekeys, the isPrekeySignatureValid returns true and prekey is not regenerated
• Malformed prekey signature by replacing its first char with 'x' - BAD_MESSAGE_MAC is found and the function returns false. Prekey regeneration is attempted.