BlendListByEnum assumes that enum values are sequential

FAnimNode_BlendListByEnum assumes that values within a custom enum type are sequential (ie. the index 0 = value 0, index 1 = value 1).  But this is not true of all custom enum types, for example:

UENUM(BlueprintType)
enum class EAnimType : uint8
{
 Default = 0,
 Type1 = 1,
 Type100 = 100,
 MAX
}; 

Here index 3 = 100 so we can't just map from the enum value directly to the pin index.  We need to go via the enum index, from the enum value.  So we need another mapping on FAnimNode_BlendListByEnum like EnumToPoseIndex but instead for EnumIndexToEnumValue.

1. Open the project on the referenced UDN
2. Follow the instructions from the licensee
   1. Expected behaviour: pressing 3 key should play T-Pose
   2. Actual behaviour: pressing 3 key plays the idle animation (same as pressing 1)