[Constaint system] Add a predicate for when to check closures in enclosing expr

Introduce a new predicate, shouldTypeCheckInEnclosingExpression(), to
determine when the body of a closure should be checked as part of the
enclosing expression rather than separately, and use it in the various
places where "hasSingleExpressionBody()" was used for that purpose.

lib/Sema/BuilderTransform.cpp

@@ -1701,6 +1701,13 @@ public:
 FunctionBuilderBodyPreCheck
 PreCheckFunctionBuilderRequest::evaluate(Evaluator &eval,
                                          AnyFunctionRef fn) const {
+  // We don't want to do the precheck if it will already have happened in
+  // the enclosing expression.
+  bool skipPrecheck = false;
+  if (auto closure = dyn_cast_or_null<ClosureExpr>(
+          fn.getAbstractClosureExpr()))
+    skipPrecheck = shouldTypeCheckInEnclosingExpression(closure);
+
   return PreCheckFunctionBuilderApplication(fn, false).run();
 }