EnhancedInput Chorded Actions do not work on higher priority mappings

Reported from Prismatic:

It appears that the Add Mapping Context function currently prioritizes low numbers over high numbers, which seems inconsistent with the function description and some parts of the source code.

1. Create a Third Person template project.
2. Make a copy of the default Input Mapping Context.
3. Remove the gamepad-related inputs from the default context, and remove the
   keyboard related inputs from the copied context, so that there is now a context
   for only keyboard, and one for only gamepad.
   In the BeginPlay of the BP_ThirdPersonCharacter, add the two mapping
   contexts using the “Add Mapping Context” node.
4. Set the Priority of the default mapping as “1”, and the priority of the copied
   mapping as “10”.
5. Play the third person map level, and try pressing a keyboard input and its
   equivalent gamepad input, and note which input is taking precedence..
6. The expected outcome would be that the gamepad input from the copied
   mapping should consume the input first as it has a higher priority than the
   default mapping for keyboard only (the function description also says this).
7. However currently the opposite seems to be true, with the lower priority number
   “1” taking precedence over “10”