Discourage constraint systems that use more unchecked forces.

This is in preparation for a change that allows unchecked-optional
values to be implicitly forced in all contexts.

Swift SVN r14704

lib/Sema/CSSimplify.cpp

@@ -1360,6 +1360,7 @@ ConstraintSystem::simplifyMemberConstraint(const Constraint &constraint) {
 
   // Try to look through UncheckedOptional<T>; the result is always an r-value.
   if (auto objTy = lookThroughUncheckedOptionalType(baseObjTy)) {
+    increaseScore(SK_UncheckedForce);
     baseTy = baseObjTy = objTy;
   }
 

lib/Sema/ConstraintSystem.h

@@ -584,6 +584,8 @@ struct SelectedOverload {
 enum ScoreKind {
   // These values are used as indices into a Score value.
 
+  /// An implicit force of an unchecked optional value.
+  SK_UncheckedForce,
   /// A user-defined conversion.
   SK_UserConversion,
   /// A non-trivial function conversion.
@@ -593,7 +595,7 @@ enum ScoreKind {
 };
 
 /// The number of score kinds.
-const unsigned NumScoreKinds = 3;
+const unsigned NumScoreKinds = 4;
 
 /// Describes the fixed score of a solution to the constraint system.
 struct Score {