At present, in the ABT we have special case logic so that the ABT->SBE lowering process will take FunctionCalls to "fail" and lower them down to EFail expressions.

Svilen proposed that we might want to explore adding a first class "Fail" expression to the ABT.

The goal of this ticket is to (1) determine if we should introduce a first class "Fail" expression to the ABT; and (2) if the answer is "yes" then implement a first class "Fail" expression and update the ABT->SBE lowering process accordingly (and remove the special case logic for lowering FunctionCalls to "fail").