Unexpected type change when parsing addition of integer to enum #969

Consider the following expression:

DayOfWeek.Monday + 1

Following #953 this expression now succeeds, but unexpectedly the type of the result is evaluated as int, rather than DayOfWeek.

Running the following expression in C# code (or C# interactive):

var day = DayOfWeek.Monday + 1

returns DayOfWeek as the type for variable day, rather than the integer backing type.