SIL: Uncurry function types within the Swift type system.

Remove uncurry level as a property of SILType/SILFunctionTypeInfo. During SIL type lowering, map a (Type, UncurryLevel) pair to a Swift CanType with the uncurried arguments as a Swift tuple. For example, T -> (U, V) -> W at uncurry level 1 becomes ((U, V), T) -> W--in reverse order to match the low-level calling convention. Update SILGen and IRGen all over the place for this representation change.

SILFunctionTypeInfo is still used in the SILType representation, but it's no longer load-bearing. Everything remaining in it can be derived from a Swift type.

This is an ABI break. Be sure to rebuild clean!

Swift SVN r5296

include/swift/SIL/SILBasicBlock.h

@@ -102,6 +102,8 @@ public:
   bbarg_iterator bbarg_end() { return BBArgList.end(); }
   const_bbarg_iterator bbarg_begin() const { return BBArgList.begin(); }
   const_bbarg_iterator bbarg_end() const { return BBArgList.end(); }
+  
+  ArrayRef<SILArgument*> getBBArgs() const { return BBArgList; }
 
   //===--------------------------------------------------------------------===//
   // Predecessors and Successors