[CS] Correctly handle InlineArray in shrink

Previously we would try the contextual type `(<int>, <element>)`,
which is wrong. Adjust the logic to only consider the element type.
While here, also allow desugaring of the contextual type to find the
element type.

Author: hamishknight

lib/Sema/CSSolver.cpp

@@ -1177,10 +1177,18 @@ void ConstraintSystem::shrink(Expr *expr) {
       }
 
       // Map or Set or any other associated collection type.
-      if (auto boundGeneric = dyn_cast<BoundGenericType>(base)) {
+      if (auto boundGeneric = base->getAs<BoundGenericType>()) {
         if (boundGeneric->hasUnresolvedType())
           return boundGeneric;
 
+        // The element type given by InlineArray is the second type.
+        if (boundGeneric->getDecl() == ctx.getInlineArrayDecl()) {
+          auto args = boundGeneric->getGenericArgs();
+          if (args.size() != 2)
+            return Type();
+          return args[1];
+        }
+
         llvm::SmallVector<TupleTypeElt, 2> params;
         for (auto &type : boundGeneric->getGenericArgs()) {
           // One of the generic arguments in invalid or unresolved.