[ConstraintSystem] Adjust impact of implicit Double <-> CGFloat conversions

- Prefer CGFloat -> Double over the other way around to avoid
  ambiguities;

- Every new conversion impacts the score by factor of number of
  previously applied conversions to make it possible to select
  solutions that require the least such conversions.

- Prefer concrete overloads with Double <-> CGFloat conversion
  over generic ones.

lib/Sema/CSSimplify.cpp

@@ -10527,7 +10527,14 @@ ConstraintSystem::simplifyRestrictedConstraintImpl(
 
   case ConversionRestrictionKind::DoubleToCGFloat:
   case ConversionRestrictionKind::CGFloatToDouble: {
-    increaseScore(SK_ImplicitValueConversion);
+    // Prefer CGFloat -> Double over other way araund.
+    auto defaultImpact =
+        restriction == ConversionRestrictionKind::CGFloatToDouble ? 1 : 2;
+
+    auto numConversions = CurrentScore.Data[SK_ImplicitValueConversion];
+    increaseScore(SK_ImplicitValueConversion,
+                  defaultImpact * (numConversions + 1));
+
     if (worseThanBestSolution())
       return SolutionKind::Error;