InputPatch parameters to patch constant functions were not using the
internal (temporary) variable type. That could cause validation errors
if the input patch had a mixture of builtins and user qualified members.
This uses the entry point's internal form.
There is currently a limitation: if an InputPatch is used in a PCF,
it must also have appeared in the main entry point's parameter list.
That is not a limitation of HLSL. Currently that situation is detected
and an "implemented" error results. The limitation can be addressed,
but isn't yet in the current form of the PR.
